Influence of the Irradiance on the Detection and Performance of PID-Affected PV-Modules - Buerhop-Lutz, Claudia; Pickel, Tobias; Wenz, F.; Zetzmann, Cornelia; Hauch, Jens; Camus, Christian; Brabec, Christoph (35th European Photovoltaic Solar Energy Conference and Exhibition, 2018)
Potential induced degradation (PID) is still a severe problem in many PV-installations and a huge financial risk for investors and plant-owners if not detected early. In previous investigations it was shown that thermography, conducted with handheld or drone mounted IR-cameras, is a fast and reliable tool to detect PID affected PV-modules on site and estimate their remaining electrical power during normal plant operation. In this work we show how to improve the sensitivity of IR- and various other imaging techniques by using the characteristic behavior of PID affected cells regarding the different excitation forces, i.e. solar irradiance for IR- and electric current for DLIT- and EL-measurements. Furthermore, we address the implications of this specific behavior by simulating the energy yield of several PID affected PV-strings based on real monitoring data for two inspected sites and suggest carrying out the measurements on site- and under failure- relevant conditions rather than standard test conditio
Keywords: Performance; Energy Yield; Thermography; Potential Induced Degradation; EL Imaging

Influence of the Module Temperature on the Performance and EL-Image of Precracked PV-Modules - Buerhop-Lutz, Claudia; Krause, M.; Winkler, T.; Hauch, Jens; Camus, Christian; Brabec, Christoph (35th European Photovoltaic Solar Energy Conference and Exhibition, 2018)
EL-imaging is a valuable tool to analyze PV-modules for the presence of cracked cells. Normally, these inspections are done in air-conditioned labs or at cool nights outdoors. However, the PV-modules are supposed to generate energy outdoors in the field. Therefore, they operate at significantly elevated temperatures which are much higher than the temperatures at the inspection time. In order to investigate the temperature influence on the performance of precracked PV-modules, EL-images and IV-curves were recorded of warm and mechanically loaded modules. The study illustrates that the performance of cracked cells changes with temperature and pressure. There is the tendency that modules at elevated temperatures perform better than those at low temperatures under the same loading situatio
Keywords: Performance; Temperature; Mechanical Load; Cracks; Electro-Luminescence (EL)

Influence of the Size Distribution of the SiC Powder Source on the Shape of the Crystal Growth Interface during PVT Growth of 4H-SiC Boules - Schultheiß, Jana; Ihle, Jonas; Nanot, S. Usseglio; Bonanomi, S.; Munoz, D. Callejo; Hammer, R.; Wellmann, Peter (Trans Tech Publications Ltd, 2024)
We compared the evolution of three different SiC sources during standard PVT growth runs. The evolution of the growing crystal and the morphological changes in the SiC source were visualized using in-situ X-ray visualization. Computer simulation was used to calculate the temperature field distributions. It is found that the densification and shrinkage of the SiC source material during the growth process can affect the growth conditions in such a way that the convexity of the growth interface is increased in an unfavorable manner. While unfavorable growth conditions can be related to thermal properties due to less favorable SiC powder evolution, predicting such behavior is a rather complex task that still relies on the support of experimental methods.
CRIS-Team Scopus Importer:2025-02-04
Keywords: mass transport; SiC PVT growth; SiC source material; temperature field

Influence of the starting materials used in the crystal growth process of CZT for gamma ray radiation applications - Zheng, Qian; Crocco, Jerome; Bensalah, Hakima; Wellmann, Peter; Osvet, Andres; Künecke, Ulrike; Dierre, Fabrice; Vela, O.; Perez, J.M.; Dieguez, E. (Journal of Crystal Growth, 2013)
The influences of two different ways of crystal growth preparations by using different starting materials on the detector properties have been investigated. The characterization has been carried out in terms of structural, optical, and electrical properties of the materials grown with the vertical gradient freeze method. The distributions of Zn and In at different axial positions with different crystals have been compared by using the Induced Coupled Plasma-Mass Spectroscopy technique. The size and density of Te inclusions within the materials have been identified by Infrared Microscopy. The luminescence behaviors have been investigated by studying the defects levels. Particularly, the current-voltage characteristics and Gamma-ray Spectroscopy have been investigated by comparing the performance of detectors achieved from different axial directions of the ingots. (C) 2013 Elsevier B.V. All rights reserved.
Keywords: Characterization; Defects; Gradient freeze technique; Semiconducting II-VI materials

Influence of Thiazole-Modified Carbon Nitride Nanosheets with Feasible Electronic Properties on Inverted Perovskite Solar Cells. - Cruz, Daniel; García Cerrillo, José; Kumru, Baris; Li, Ning; Perea, Jose Dario; Schmidt, Bernhard V. K. J.; Lauermann, Iver; Brabec, Christoph; Antonietti, Markus (Journal of the American Chemical Society, 2019)
Effective, solution-processable designs of interfacial electron-transporting layers (ETLs) or hole-blocking layers are promising tools in modern electronic devices, e.g., to improve the performance, cost, and stability of perovskite-based solar cells. Herein, we introduce a facile synthetic route of thiazole-modified carbon nitride with 1.5 nm thick nanosheets which can be processed to a homogeneous, metal-free ETL for inverted perovskite solar cells. We show that thiazole-modified carbon nitride enables electronic interface enhancement via suppression of charge recombination, achieving 1.09 V in Voc and a rise to 20.17 mA/cm2 in Jsc. Hence, this report presents the successful implementation of a carbon-nitride-based structure to boost charge extraction from the perovskite absorber toward the electron transport layer in p-i-n devices

Influence of tin oxide decoration on the junction conductivity of silver nanowires - Vogl, Lilian; Kalancha, Violetta; Schweizer, Peter; Denninger, Peter; Wu, Mingjian; Brabec, Christoph; Forberich, Karen; Spiecker, Erdmann (Nanotechnology, 2023)
Flexible electrodes using nanowires (NWs) suffer from challenges of long-term stability and high junction resistance which limit their fields of applications. Welding via thermal annealing is a common strategy to enhance the conductivity of percolated NW networks, however, it affects the structural and mechanical integrity of the NWs. In this study we show that the decoration of NWs with an ultrathin metal oxide is a potential alternative procedure which not only enhances the thermal and chemical stability but, moreover, provides a totally different mechanism to reduce the junction resistance upon heat treatment. Here, we analyze the effect of SnO x decoration on the conductance of silver NWs and NW junctions by using a four-probe measurement setup inside a scanning electron microscope. Dedicated transmission electron microscopy analysis in plan-view and cross-section geometry are carried out to characterize the nanowires and the microstructure of the junctions. Upon heat treatment the junction resistance of both plain silver NWs and SnO x -decorated NWs is reduced by around 80%. While plain silver NWs show characteristic junction welding during annealing, the SnO x -decoration reduces junction resistance by a solder-like process which does not affect the mechanical integrity of the NW junction and is therefore expected to be superior for applications.
CRIS-Team Scopus Importer:2023-02-24
Keywords: electrical measurements; electron microscopy; junctions; nanowires

Influence of µCT scanning resolution and volume on FEM-simulation of periodic 3D-printed porous ceramics - Biggemann, Jonas; Köllner, David; Schatz, Jonas; Stumpf, Martin; Fey, Tobias (Materials Letters, 2021)
Complex cellular ceramic structures are commonly fabricated via replica technique, gel-casting, or freeze-drying. These structures exhibit a manufacturing-related heterogeneity in their microstructure associated with a large scattering range of their physical properties. This further complicates the determination of the representative volume-of-interest (VOI) for the corresponding characterization method. Periodic cellular ceramics can be systematically investigated by µCT analysis to determine the influence of the scan resolution on the results of the mechanical FEM simulation under the same boundary conditions (load, displacement). In this work, a complex 3D printed Al2O3 structure with 3×3×3 arranged cubic unit cells is scanned with three different µCT resolutions (6.87 µm, 13.56 µm and 27.11 µm). From the scans, FE models and sub-volumes are created with a gradation by a factor of 2 down to 1/8 of the initial volume to determine the representative VOI. It was demonstrated that a good agreement with the experimental data can only be achieved with the highest scanning resolution, but here a reduction of the VOI by a factor of four is possible to obtain identical results despite slight production-related deviations.
CRIS-Team Scopus Importer:2021-08-13
Keywords: Additive manufacturing; FEM-simulation; Microstructure; Tomography; Volume of interest

Infrared Absorption Imaging of Water Ingress Into the Encapsulation of (Opto-)Electronic Devices - Hepp, Johannes; Vetter, Andreas; Langner, Stefan; Woiton, Michael; Jovicic, Gordana; Burlafinger, Klaus; Hauch, Jens; Camus, Christian; Egelhaaf, Hans-Joachim; Brabec, Christoph (IEEE Journal of Photovoltaics, 2019)
Water ingress into the encapsulation of electronic devices is a serious issue, especially for organic and perovskite-based electronics. In order to guide the development of suitable barrier materials and design, a reliable, fast, and non-destructive analysis tool is required. In this work, an imaging setup is presented, which is based on selective infrared (IR) radiation sources and a mid-IR sensitive camera that uses the absorption hand of water around 1920 nm and a reference band. This system enables us to monitor the distribution of water concentration inside the packaging of devices and its change over time. Our measurement is capable of detecting the local presence of water down to the mg/m(2) concentration range in a wide variety of encapsulation materials. The new tool allows identifying the pathways of moisture ingress into the encapsulation along with the corresponding diffusion coefficient. Thus, it provides fast and reliable analysis of humidity related failure mechanisms, and consequently helps to improve the design of encapsulation materials and processes.
Keywords: Degradation; diffusion processes; optical signal detection; organic photovoltaics (PVs); packaging

In(iii)-dictated formation of double Cs2AgxNa1−xFeyIn1−yCl6 perovskites - Stroyuk, Oleksandr; Raievska, Oleksandra; Barabash, Anastasia; Hauch, Jens; Brabec, Christoph (Journal of Materials Chemistry C, 2023)
Stable double Cs2AgxNa1−xFeyIn1−yCl6 (CANFIC) microcrystalline perovskites were produced in air-open conditions. In(iii) was found to steer the precursor interaction exclusively towards single-phase solid-solution CANFIC perovskite microcrystals with well-controlled composition, even when present at a small amount (1%). CANFICs revealed sensitivity in the visible range with the lowest bandgap of 1.95 eV found for y = 0.99. Due to a combination of open-environment synthesis conditions, reliable compositional control, the abundant and relatively non-toxic character of constituents, stability, and absorbance in the visible spectral range, CANFIC perovskites show high promises for photovoltaic and photochemical applications.
CRIS-Team Scopus Importer:2023-06-23

Inkjet printed organic and perovskite photovoltaics—review and perspectives - Maisch, Philipp; Tam, Kai Cheong; Jang, DongJu; Steinberger, Marc; Yang, Fu; Brabec, Christoph; Egelhaaf, Hans-Joachim (Organic Flexible Electronics, 2021)
This chapter provides a review on digital printing of organic solar cells (OSCs) and perovskite solar cells (PSCs). It starts with a brief introduction to the fundamentals of both solar technologies. Highlighting the specific demands of many novel solar applications, the necessity to fabricate devices using cheap and most versatile techniques, such as drop-on-demand inkjet, is outlined. A short discussion on the fundamentals of inkjet technology provides the background for a literature overview on digitally printed OSCs and PSCs. The main part of this chapter describes the most significant achievements in the field and remaining challenges for inkjet fabrication of active layers, electron- as well as hole-transport layers and electrodes. An outlook on the perspectives that the combination of printed photovoltaics and inkjet has to offer concludes the chapter.<br
Keywords: Inkjet; organic photovoltaics; OPV; OSC; perovskite photovoltaics; PSC; printed solar cell; solar module; flexible electrode

Inkjet-printed polymer-based scattering layers for enhanced light outcoupling from top-emitting organic light-emitting diodes - Heinrichsdobler, Armin; Engelmayer, Manuel; Riedel, Daniel; Brabec, Christoph; Wehlus, Thomas (Proceedings Volume 10362, Organic Light Emitting Materials and Devices XXI; 103622B (2017), 2017)
High refractive index polymer-based scattering layers used as internal light extraction layers are a promising low-cost approach to enhance the luminous efficacy of organic light-emitting diodes (OLEDs). In order to avoid damaging of the OLED layers a structured and contactless deposition method for the polymer-based scattering layers is required. For enhanced lifetime of the devices the water diffusion through the scattering layer has to be eliminated by a structured patterning technique. Inkjet printing offers both a contactless and structured deposition. In this study we evaluate inkjet printing of nanocomposite polymer-based scattering layers for OLEDs. A detailed view on the material and process development is given. This involves an optimization of ink formulation, printing parameters as well as layer formation. The resulting haze values of the scattering layers at 550 nm vary between 40% and 90% for different layer thicknesses. The gain in external quantum efficacy of top-emitting OLEDs induced by light scattering compared to reference devices peaks at a factor of 2.3. The obtained results are discussed and verified by an optical volume scattering simulation model which will be presented in full detail. Also a parameter variation study and its impact on extraction efficiency will be shown.

Inkjet printed silver nanowire percolation networks as electrodes for highly efficient semitransparent organic solar cells - Maisch, Philipp; Tam, Kai Cheong; Lucera, Luca; Egelhaaf, Hans-Joachim; Scheiber, Horst; Maier, Eugen; Brabec, Christoph (Organic Electronics, 2016)
In this work, we demonstrate inkjet printing of silver nanowires (AgNW) with an average length of 10's of μm using industrial printheads with nozzle diameters in the same size range. The printed silver nanowire mesh reveals uniform distribution and a good balance between conductivity and transmittance, which is comparable to layers fabricated by conventional methods like slot-die or spray coating. Employing a novel AgNW ink formulation based on a high boiling alcohol allows printing directly on PEDOT:PSS and prevents nozzle clogging. Using silver nanowire meshes as bottom and top electrodes, a fully inkjet printed semitransparent organic solar cell with a power conversion efficiency of 4.3% for 1 cm area is demonstrated, which is the highest value reported so far for fully inkjet printed organic photovoltaic cells.
Keywords: Inkjet; Nanowire; Organic photovoltaics; Semitransparent electrode

Inkjet printing of highly conductive nanoparticle dispersions for organic electronics - Maisch, Philipp; Tam, Kai Cheong; Fecher, Frank W.; Egelhaaf, Hans Joachim; Brabec, Christoph; Scheiber, Horst; Maier, Eugen (12th International Congress on Molded Interconnect Devices, MID 2016, 2016)
Inkjet printing of conductive nanoparticle dispersions and their use in organic electronic devices for multiple purposes like contact pads and electrodes is demonstrated. In this context, we show the printing of semitransparent silver grid/Poly(3,4-ethylene-dioxythiophene) :poly(styrenesulfonate) (PEDOT:PSS) electrodes and their application in organic photovoltaics (OPV). The cell performance was optimized using finite element simulations accounting for electrical and optical layer properties as well as resolution restrictions given by the inkjet. Furthermore, we demonstrate inkjet printing of silver nanowires (AgNW) and their use as percolation electrode. Characterization reveals low sheet resistance of less than 20 Ω/□ together with a high specular transmittance of more than 90 %, indicating the excellent quality of the inkjet printed layers. Applying them as cathode and anode, fully inkjet printed semitransparent solar cells with power conversion efficiencies (PCE) of up to 4.3 % on an active area of > 1 cm are demonstrated.
Keywords: inkjet; organic photovoltaics; PEDOT:PSS; semitransparent electrode; silver grid; silver nanowires

Inkjet printing of multiple layers for large-scale, cadmium-free quantum dot light-emitting diodes - Hübner, Tobias; Brabec, Christoph; Göötz, Britta; Von Malm, Norwin (Proceedings of SPIE - The International Society for Optical Engineering, 2020)
Quantum Dot Light Emitting Diodes (QDLEDs) are a promising alternative to the already established organic LEDs (OLEDs) in applications like automotive rear-lights. QDLEDs can exhibit higher luminance characteristics and superior operational stability. In order to be able to transfer the QDLEDs from their research state into market products, the oftenused Cadmium-containing QDs must be replaced by less toxic alternatives. Furthermore, the processing costs for the QDLEDs have to be minimized. We overcome both challenges by utilizing Indium Phosphide based QDs in the devices and applying inkjet-printing as a low-material consumption deposition technique. Inkjet-printing three layers of the stack design on top of each other proofs to be challenging concerning the layers homogeneity both macroscopically as well as microscopically. We present viable approaches for the ink formulation process, substrate-pretreatment steps and printing strategies to overcome wetting, dewetting and coffee-staining issues. The printed layers are investigated via topological and fluorescent tools and the successfully fabricated devices are examined via electrooptical measurements.
CRIS-Team Scopus Importer:2020-06-02
Keywords: Area light source; Indium phosphide quantum dots; Inkjet-printing multiple layers; Quantum dot LEDs

Inkjet printing of semitransparent electrodes for photovoltaic applications - Maisch, Philipp; Tam, Kai C.; Lucera, Luca; Fecher, Frank W.; Egelhaaf, Hans-Joachim; Scheiber, Horst; Maier, Eugen; Brabec, Christoph (7th Conference on Organic Photovoltaic Devices, 2016)
In this work we compare two different semitransparent inkjet printed electrodes for organic photovoltaic (OPV) applications. We highlight the processing as well as layer properties of the most commonly used silver grid/PEDOT:PSS electrodes and a newly developed inkjet printed silver nanowire (AgNW) mesh. Application of the different electrode types in fully inkjet printed organic solar cells reveals the superior performance of the AgNWs. Using them as bottom and top electrode, semitransparent solar cells with power conversion efficiencies (PCE) of up to 4.3 % are demonstrated. Comparable devices with silver grid electrodes reach a maximum PCE of 3.6 %. We identify shading of the opaque silver grids, which cover ∼10 % of the device area, and thermal stress introduced by the curing of the silver grid top electrodes as main factors for the losses. Furthermore, the silver grids do not only lower the short circuit current of the solar cell, but are also visually obstructive. The newly developed inkjet printed AgNW percolation network electrodes show high transparency of over 90 % at a sheet resistance of less than 20 ω/□ and a very low haze of less than 3 %. This enables a clear view through semitransparent devices like organic light emitting diodes (OLEDS) or solar cells in which they can be use
Keywords: Inkjet; Organic photovoltaics; PEDOT:PSS; Semitransparent electrode; Silver grid; Silver nanowires

Innovative architecture design for high performance organic and hybrid multi-junction solar cells - Li, Ning; Spyropoulos, George D.; Brabec, Christoph (Proceedings Volume 10363,Organic, Hybrid, and Perovskite Photovoltaics XVIII, 2017)
The multi-junction concept is especially attractive for the photovoltaic (PV) research community owing to its potential to overcome the Schockley-Queisser limit of single-junction solar cells. Tremendous research interests are now focused on the development of high-performance absorbers and novel device architectures for emerging PV technologies, such as organic and perovskite PVs. It has been predicted that the multi-junction concept is able to boost the organic and perovskite PV technologies approaching the 20% and 30% benchmarks, respectively, showing a bright future of commercialization of the emerging PV technologies. In this contribution, we will demonstrate innovative architecture design for solution-processed, highly functional organic and hybrid multi-junction solar cells. A simple but elegant approach to fabricating organic and hybrid multi-junction solar cells will be introduced. By laminating single organic/hybrid solar cells together through an intermediate layer, the manufacturing cost and complexity of large-scale multi-junction solar cells can be significantly reduced. This smart approach to balancing the photocurrents as well as open circuit voltages in multi-junction solar cells will be demonstrated and discussed in detai

Inorganic Halide Perovskite Solar Cells: Progress and Challenges - Tian, Jingjing; Xue, Qifan; Yao, Qin; Li, Ning; Brabec, Christoph; Yip, Hin-Lap (Advanced Energy Materials, 2020)
All-inorganic perovskite semiconductors have recently drawn increasing attention owing to their outstanding thermal stability. Although all-inorganic perovskite solar cells (PSCs) have achieved significant progress in recent years, they still fall behind their prototype organic–inorganic counterparts owing to severe energy losses. Therefore, there is considerable interest in further improving the performance of all-inorganic PSCs by synergic optimization of perovskite films and device interfaces. This review article provides an overview of recent progress in inorganic PSCs in terms of lead-based and lead-free composition. The physical properties of all-inorganic perovskite semiconductors as well as the hole/electron transporting materials are discussed to unveil the important role of composition engineering and interface modification. Finally, a discussion of the prospects and challenges for all-inorganic PSCs in the near future is presented.
CRIS-Team Scopus Importer:2020-05-12
Keywords: inorganic perovskite; lead-based; lead-free perovskites; perovskite solar cells; perovskites

In Situ and Ex Situ Energy-Filtered Transmission Electron Microscopy Studies on the Nanomorpholgy Evolution of Organic Bulk Heterojunction Solar Cells - Harreiß, Christina; Langner, Stefan; Berlinghof, Marvin; Rechberger, Stefanie; Will, Johannes; Unruh, Tobias; Brabec, Christoph; Spiecker, Erdmann (Microscopy and Microanalysis, 2019)

In situ bow reduction during sublimation growth of cubic silicon carbide - Kollmuß, Manuel; Mauceri, Marco; Roder, Melissa; La Via, Francesco; Wellmann, Peter (Reviews on Advanced Materials Science, 2022)
Sublimation growth of cubic silicon carbide (3C-SiC) with diameters of 50 and 100 mm was performed on freestanding homoepitaxial grown seeds. For both seeds and sublimation grown crystals, two different relaxation axes with varying curvature could be observed with the higher bent axis aligned perpendicular to the original wafer flat. A general reduction in the wafer bow independent of the starting curvature and size of the seeds could be observed. Using the X-ray imaging, we could observe in situ that the bow reduction is linked to the growth of new material and cannot be initiated by heat up or cool down processes alone. Raman spectroscopy of the grown crystals revealed that the observed flattening goes along with a tensing of the seeding layers while the surface of the crystals remains free of a stress gradient. A slight concave bending of lattice planes along the main relaxation axis could be observed by high-resolution XRD rocking curve measurements while for the lower bent axis, no lattice plane bending occurred. Full width half maximum values of the (002) reflection showed values as low as 67 arcseconds proofing the possibility to grow large-area, high-quality 3C-SiC using sublimation growth.
CRIS-Team WoS Importer:2023-01-27

In situ characterization methods for evaluating microstructure formation and drying kinetics of solution-processed organic bulk-heterojunction films - Güldal, Nusret Sena; Kassar, Thaer; Berlinghof, Marvin; Unruh, Tobias; Brabec, Christoph (Journal of Materials Research, 2017)
Recently, in situ characterization methods have attracted increasing attention, especially in organic photovoltaics (OPV) field, since they provide greater insight into the mechanism of film formation, thus help to identify optimized processing conditions used to process the most efficient organic bulk-heterojunction thin films. In combination with various powerful X-ray-based characterization methods, several studies observed the morphological changes under the influence of different processing conditions. In this review, we summarize the fundamentals and implementation of X-ray-based and optical characterization methods, utilized in in situ mode and introduce the reader a better overview of the information acquired from a given technique in terms of microstructure formation in OPV. While we give a chronological development of in situ characterization methods in the field of OPV, we discuss the interplay between thermodynamics of solutions and drying kinetics of different types of organic blends. © 2017 Materials Research Society.
Keywords: Characterization; Drying; Heterojunctions; Microstructure; Thermodynamics; Thin films; Characterization methods; In-situ characterization; Microstructure formation; Optical characterization; Organic bulk heterojunctions; Organic photovoltaics; Photovoltaic; Thermodynamics of solutions; In situ processing

In-situ Er-doping of SiC bulk single crystals - Müller, Ralf; Desperrier, Patrick; Seitz, Christoph; Weißer, Matthias; Magerl, Andreas; Maier, Manfred; Winnacker, Albrecht; Wellmann, Peter (Materials Science Forum, 2004)
In this work the first PVT grown in-situ erbium doped SiC bulk crystal, to our knowledge, is presented. The crystal was characterised by secondary ion mass spectrometry (SIMS) and photoluminescence measurements. SIMS investigations show erbium concentrations in the range of 1.1 (.) 10" cm(-3) to 2.9 (.) 10(14) cm(-3). photoluminescence measurements between 1450 run and 1650 nm were conducted at 19 K, 77 K and 300 K. A distinct luminescence at 1540 nm corresponding to the 4 I-4(13/2) –> I-4(15/2) transition was detected even at room temperature. In the investigated temperature range, luminescence intensity shows only, a slight decrease of 16 %. Measurements with different laser powers suggest a saturation of erbium related luminescence in our experimental condition
Keywords: Erbium; PVT Method; Rare Earth Doping; SiC Bulk Growth

In Situ Monitoring of the Ambient Gas Phase during PVT Growth of Nominally Undoped High Resistivity SiC Boules - Ihle, Jonas; Wellmann, Peter (Trans Tech Publications Ltd, 2023)
The aim of this study is to show the applicability of continuous residual gas analysis for growth monitoring of undoped SiC with physical vapor transport (PVT). For this purpose, two crystals were grown, one without doping and one with continuous nitrogen doping. During the processes continuous residual gas analysis were conducted and evaluated with emphasis on the temporal variations of the nitrogen content. The charge carrier concentration of the final crystals wasdetermined by optical methods (spectrally resolved absorption measurement with UV-VIS and Raman spectroscopy) and the results were compared with the residual gas analysis during growth. A correlation was found between the measured nitrogen-related signal and the charge carrier concentration in the samples.
CRIS-Team Scopus Importer:2023-10-06
Keywords: 4H-SiC; high resistivity SiC; PVT; residual gas analysis; unintentional background doping

In Situ Monitoring of Unintentionally Released Nitrogen Gas in the Initial PVT Silicon Carbide Growth Process Using Mass Spectrometry - Ihle, Jonas; Wellmann, Peter (Materials Science Forum, 2022)
Different initial process steps during PVT crystal growth of SiC were monitored with a mass spectrometer. To measure the gas phase composition in the PVT growth machine during these steps the continuously pumped exhaust gas was analyzed by a quadrupole mass spectrometer (PrismaPro QMG 250). In order to reduce unintentionally doping of the crystal by contaminations in the growth setup the focus was on the release of nitrogen during the initial steps of the growth process. During the heat up of the growth setup in vacuum a substantial release of molecular nitrogen was observed at 800 °C. Further, the influence of pump and purge-steps on the amount of nitrogen in the gas phase was examined. After performing a pump and purge step, the intensity of the measurable nitrogen-related signal (m/z = 28) was approximately 20 % of the initial value. In-situ monitoring of the gas phase during the initial steps of crystal growth proved to be a versatile tool for the development of a process minimizing unintentionally doping through released nitrogen.
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Keywords: 4H-SiC; nitrogen adsorption; PVT; residual gas analysis; unintentional background doping

In Situ Monitoring Technologies as Prospective Validation Tools for Numerical Simulations of Ammonothermal Crystal Growth - Schimmel, Saskia; Salamon, Michael; Tomida, Daisuke; Kobelt, Ines; Heinlein, Lukas; Kimmel, Anna-Carina; Steigerwald, Thomas; Ishiguro, Tohru; Honda, Yoshio; Chichibu, Shigefusa F.; Amano, Hiroshi; Schlücker, Eberhard; et al. (7th European Conference on Crystal Growth, 2022)

In-situ observation of mass transfer in the CF-PVT growth process by X-ray imaging - Chaussende, D.; Wellmann, Peter; Ucar, M.; Pons, Michel; Madar, R. (Materials Science Forum, 2006)
The development of the Continuous Feed Physical Vapour Transport (CF-PVT) process requires a perfect control of each phenomenon in the growth cell. Along this line, the present paper gives some inputs on the CF-PVT mass transfer regimes with respect to the process parameters, both from qualitative and quantitative viewpoints. For example, two boundary cases have been evidenced depending on the temperature. At low temperature, the growth is limited by the sublimation step between the source and the seed. In this case, the CF-PVT process can be roughly assimilated to the classical seeded sublimation technique. At high temperature, the process is limited by the feeding step, i.e. the CVD deposition and infiltration on the lower part of the source. Measurements are correlated to in-situ X-ray imaging. The ability of the X-ray imaging to in-situ qualify and quantify the mass transfer is discusse
Keywords: Bulk Growth; HTCVD; Mass Transfer; Sublimation; X-Ray

In-situ Observation of Polytype Switches During SiC PVT Bulk Growth by High Energy X-ray Diffraction - Wellmann, Peter; Konias, Katja; Hens, Philip; Hock, Rainer; Magerl, Andreas (Materials Science Forum, 2009)
This work reports on the in-situ observation of a polytype switch during physical vapor transport (PVT) growth of bulk SiC crystals by x-ray diffraction. A standard PVT reactor for 2 '' and 3 '' bulk growth was set up in a high-energy x-ray diffraction lab. Due to the high penetration depth of the high-energy x-ray beam no modification of the PVT reactor was necessary in order to measure Laue diffraction patterns of the growing crystal with good signal to noise ratio. We report for the first time upon the in-situ observation of polytype switching during SiC bulk PVT growt
Keywords: bulk crystal growth; physical vapor transport; in-situ growth control; polytypes

In-situ phase formation study of copper indium diselenide absorber layers from CuIn nanoparticles and evaporated selenium - Möckel, Stefan; Hölzing, Astrid; Hock, Rainer; Wellmann, Peter (Thin Solid Films, 2013)
In this work CuInSe (CISe) thin films were fabricated by rapid thermal processing of printed CuIn nanoparticles and thermally evaporated selenium as precursor layer. Research is focused on real-time investigations such as in-situ X-ray diffraction and dynamic scanning calorimetry. These measurements show CISe formation starting at 300 C. Significant amount of intermediate phases as reported for state-of-the-art rapid thermal processing of stacked elemental layer was not observed. The morphology of the nanoparticulate layers was examined by field emission scanning electron microscopy. Grain size developed from nanosized binary CuIn nanoparticles to microsized CISe grains. Porosity decreases in the temperature range from 340 C to 540 C. © 2012 Elsevier B.V.
Keywords: Chalcopyrite; CuInSe2; Dynamic scanning calorimetry; Intermetallic nanoparticles; Real-time investigation; XRD

In Situ Probing the Crystallization Kinetics in Gas-Quenching-Assisted Coating of Perovskite Films - Qiu, Shudi; Majewski, Martin; Dong, Lirong; Jang, Dongju; Le Corre, Vincent Marc; García Cerrillo, José; Ronsin, Olivier J.J.; Yang, Fu; Guo, Fei; Zhang, Kaicheng; Lüer, Larry; Harting, Jens; et al. (Advanced Energy Materials, 2024)
The pursuit of commercializing perovskite photovoltaics is driving the development of various scalable perovskite crystallization techniques. Among them, gas quenching is a promising crystallization approach for high-throughput deposition of perovskite films. However, the perovskite films prepared by gas-quenching assisted blade coating are susceptible to the formation of pinholes and frequently show inferior crystallinity if the interplay between film coating, film drying, and crystallization kinetics is not fully optimized. That arguably requires a thorough understanding of how single processing steps influence the crystallization kinetics of printed perovskite films. Here, in situ optical spectroscopies are integrated into a doctor-blading setup that allows to real-time monitor film formation during the gas-quenching process. It is found that the essential role of gas quenching treatment is in achieving a smooth and compact perovskite film by controlling the nucleation rate. Moreover, with the assistance of phase-field simulations, the role of excessive methylammonium iodide is revealed to increase grain size by accelerating the crystal growth rate. These results show a tailored control of crystal growth rate is critical to achieving optimal film quality, leading to fully printed solar cells with a champion power conversion efficiency of 19.50% and mini solar modules with 15.28% efficiency are achieved.
CRIS-Team Scopus Importer:2024-01-12
Keywords: blade coating; fully printed perovskite photovoltaics; gas quenching; in situ techniques; phase-field simulations

'In situ synthesis' of source material from elemental Si and C during SiCPVT growth process and characterization using digital X-ray imaging - Wellmann, Peter; Herro, Ziad Georges; Straubinger, Thomas; Winnacker, Albrecht (Materials Science Forum, 2002)
Silicon Carbide (SiC) single crystals grown by the physical vapor transport technique usually use SiC powder as source material which was synthesized in a previous technological step. We have investigated the possibility to combine the SiC synthesis and SiC crystal growth into one process. Using a SiC wafer on top of the source material which shields the SiC seed from the exothermal Si + C insitu synthesis we were able to grow SiC crystals with structural properties comparable to the conventional process; i.e. 40mm 6H-SiC single crystal diameter and micropipe density <200cm(-2
Keywords: In Situ Synthesis; Physical Vapor Transport Growth; Source Material; X-Ray Imaging

In situ visualization and analysis of silicon carbide physical vapor transport growth using digital X-ray imaging - Wellmann, Peter; Bickermann, Matthias; Hofmann, Heinz-Dieter; Kadinski, Lev; Selder, Markus; Straubinger, Thomas; Winnacker, Albrecht (Journal of Crystal Growth, 2000)
Using digital X-ray imaging we have investigated the on-going processes during physical vapor transport growth of SiC. A high-resolution and high-speed X-ray detector based on image plates and digital recording has been used to monitor SiC bulk crystal growth as well as SiC source material degradation on-line during growth. We have analyzed the shape of the growth interface and the evolution of the SIC source morphology. The crystal growth process will be discussed in terms of growth rate and limitations of the physical vapor transport of SIC gas species from the source to the growth interface, (C) 2000 Elsevier Science B.V. All rights reserved.
Keywords: SiC; Physical vapor transport; X-ray imaging

In Situ Visualization of GaN Crystals in Ammonothermal High Pressure Autoclaves by X-ray Imaging - Schimmel, Saskia; Künecke, Ulrike; Steigerwald, Thomas; Hertweck, Benjamin; Alt, Nicolas; Schlücker, Eberhard; Wellmann, Peter (German Conference on Crystal Growth, 2014)

In situ visualization of SiC physical vapor transport crystal growth - Wellmann, Peter; Herro, Ziad Georges; Winnacker, Albrecht; Püsche, Roland; Hundhausen, Martin; Masri, P.; Kulik, A.; Bogdanov, M.; Karpov, S.; Ramm, M.; Makarov, Y. (Journal of Crystal Growth, 2005)
We review a digital X-ray imaging technique which permits in situ 2D imaging of the crucible interior during physical vapor transport growth of SiC. In addition, we use 13C-labeling experiments to determine the mass transport paths in the growth cell interior. The combination of both experimental techniques enabled the analysis of the global SiC growth process like determination of growth rate, quantitative analysis of the evolution of the source material morphology, interaction of Si- and C-containing gas species with the graphite crucible wall, etc. The data will be used for comparison with numerical modeling of the SiC growth process including calculation of temperature field, mass transport and changes of the source material morphology, i.e. porosity and graphitization. In addition to the application of X-ray imaging for fundamental growth studies, monitoring of routine growth runs will also be pointed out. © 2004 Elsevier B.V. All rights reserved.
UnivIS-Import:2015-03-09:Pub.2005.nat.dphy.IAP.exphys.insitu
Keywords: Characterization; Computer simulation; Growth from vapor; Semiconducting silicon compounds

In Situ Visualization of the Ammonothermal Crystallization Process by X-ray Technology - Schimmel, Saskia; Wellmann, Peter (Ammonothermal Synthesis and Crystal Growth of Nitrides, 2021)
X-ray based in situ monitoring techniques for ammonothermal processes are reviewed. Technological aspects are discussed, including general aspects of in situ X-ray visualization technology as well as the corrosion resistance of prospective materials for X-ray transparent windows under ammonothermal conditions (for more comprehensive information on corrosion resistance see Chap. 11). In situ X-ray visualization methods have proven to be extremely useful for gaining insights that are inaccessible through other methods to date. Results obtained by in situ X-ray imaging comprise information on solubility and dissolution kinetics as well as insights into the transport of solutes and local concentration changes of solutes. Moreover, phase changes of the fluid can be monitored and the technique has been adapted for solubility studies of novel materials that are unavailable as bulk materials to date. Findings of particular interest include a revision of solubility data for GaN, insights into face-selective and mineralizer-selective dissolution kinetics of GaN, and the visualization of Ga transport within the fluid upon dissolution of GaN. The observed extremely slow motion of Ga-containing species suggests a pronounced influence of solutes on the viscosity of the fluid, which has largely been treated as negligible due to the lack of data for the respective mixtures so fa
Keywords: ammonothermal synthesis; in situ visualization; in situ x-ray; crystal growth of nitrides; solubitity; dissolution kinetics; Ga transport

In-situ X-ray diffraction analysis of the recrystallization process in Cu2ZnSnS4nanoparticles synthesised by hot-injection - Brandl, Marco; Ahmad, Rameez; Distaso, Monica; Azimi, Seyed Hamed; Hou, Yi; Peukert, Wolfgang; Brabec, Christoph; Hock, Rainer (Thin Solid Films, 2015)
Kesterite CuZnSnS(CZTS) is a promising material for thin film solar cell applications. The biggest advantages of this compound lie in the abundance and non-toxicity of the contained elements. Low temperature hot injection synthesis can provide an economic way to produce CZTS nanoparticles for application in solution processed solar cells. Powder X-ray diffraction (PXRD) measurements on the as-synthesised particles suggest that the crystal structure is cubic and can be best described as sphalerite-like. This means that the cations in the CZTS are statistically distributed on the cation sites of the crystal lattice rather than well-ordered like in the tetragonal kesterite structure. An in-situ PXRD measurement while annealing the particles up to 550 °C revealed a recrystallization process that transforms the structure from cubic to tetragonal meaning an ordering of the cations.
Keywords: Copper zinc tin sulphide; Cubic phase; Hot-injection synthesis; In-situ; Phase transition; Tetragonal phase; X-ray diffraction

In-Situ X-ray Diffraction Analysis of the Recrystallization Process in Cu2ZnSnS4 Nano Particles Synthesized by Hot-Injection - Brandl, Marco; Ahmad, Rameez; Distaso, Monica; Azimi, Hamed; Hou, Yi; Peukert, Wolfgang; Brabec, Christoph; Hock, Rainer (Thin Solid Films, 2015)
Kesterite Cu2ZnSnS4 (CZTS) is a promisingmaterial for thin film solar cell applications. The biggest advantages of this compound lie in the abundance and non-toxicity of the contained elements. Low temperature hot injection synthesis can provide an economic way to produce CZTS nanoparticles for application in solution processed solar cells. Powder X-ray diffraction (PXRD) measurements on the as-synthesised particles suggest that the crystal structure is cubic and can be best described as sphalerite-like. This means that the cations in the CZTS are statistically distributed on the cation sites of the crystal lattice rather than well-ordered like in the tetragonal kesterite structure. An in-situ PXRD measurement while annealing the particles up to 550 °C revealed a recrystallization process that transforms the structure from cubic to tetragonal meaning an ordering of the cations.
EAM Import::2019-03-13

In-situ X-ray measurements of defect generation during PVT growth of SiC - Konias, Katja; Hock, Rainer; Stockmeier, Matthias; Wellmann, Peter; Miller, Michael; Ossege, Stefan; Magerl, Andreas (Materials Science Forum, 2007)
A standard inductively heated PVT growth furnace modified for diffraction experiments with high energy x-rays in focussing Laue geometry was built. The growth furnace will be placed in front of a tungsten anode high energy x-ray source. The Laue diffraction pattern of the growing crystal can be detected on a CCD camera detector. Evolution of crystalline defects as a function of the growth process parameters will be infered from the diffraction experiments. The furnace design and results of first test measurements serving as proof of concept are reporte
Keywords: PVT; crystal growth; growth furnace; x-ray diffraction; high energy x-rays; focussing Laue geometry; defects

In situ X-ray monitoring of transport and chemistry of Ga-containing intermediates under ammonothermal growth conditions of GaN - Schimmel, Saskia; Duchstein, Patrick; Steigerwald, Thomas; Kimmel, Anna-Carina; Schlücker, Eberhard; Zahn, Dirk; Niewa, Rainer; Wellmann, Peter (Journal of Crystal Growth, 2018)
Formation and transport of Ga-containing intermediates are essential for ammonothermal bulk growth of GaN. In this work, in situ X-ray transmission measurements are established as a tool for monitoring face-selective dissolution of GaN crystals as well as the Ga-concentration in the fluid. The accuracy of concentration determination by X-ray transmission measurements is evaluated and the detection limit for dissolved species is estimated. The detection limit is given both as a gallium concentration and as an attenuation coefficient, thus, it can easily be transferred to other materials of interest. Face-selective ammonothermal etching is investigated for both ammonoacidic and ammonobasic mineralizers. Time- and space-resolved monitoring of the concentration of Ga-containing intermediates is demonstrated using NH4F mineralizer. The results are discussed with respect to the formation of Ga-containing intermediates and mechanisms of mass transport. Based on molecular dynamics simulations, the experimentally observed, unexpectedly low diffusion coefficient for the Ga-transporting species is ascribed at least partially to the diffusion of larger [GaxFy]3x−y aggregates.<br
Keywords: Diffusion; Mass transfer; Growth from solutions; Gallium nitride; Solvents; Ammonothermal crystal growth

Instantaneous charge separation in non-fullerene acceptor bulk-heterojunction of highly efficient solar cells - Franco, V. A. Camargo; Gasparini, Nicola; Nagahara, Tetsuhiko; Lueer, Larry; Cerullo, Giulio; Brabec, Christoph (205, 2019)
Using broadband transient absorption in a high efficiency (>11%) photovoltaic blend with a non-fullerene acceptor, we observe instantaneous (sub-30 fs) charge separation, demonstrating close to ideal donor-acceptor level matching and nanomorphology in this ble

Integrated molecular, morphological and interfacial engineering towards highly efficient and stable solution-processed small molecule solar cells - Min, Jie; Luponosov, Yuriy N.; Gasparini, Nicola; Xue, Lingwei; Drozdov, Fedor V.; Peregudova, Svetlana M.; Dmitryakov, Petr V.; Gerasimov, Kirill L.; Anokhin, Denis V.; Zhang, Zhi-Guo; Ameri, Tayebeh; Chvalun, Sergei N.; et al. (Journal of Materials Chemistry A, 2015)
The synthesis of a series of A-π-D-π-A oligomers bearing coplanar electron-donating dithieno[3,2-b:2′,3′-d]silole (DTS) unit linked through bithiophene π-bridges with the electron-withdrawing alkyldicyanovinyl (alkyl-DCV) groups is described. This study demonstrates a systematic investigation of structure-property relationships in this type of oligomer and shows obvious benefits of alkyl-DCV groups as compared to the commonly used DCV ones, in terms of elaboration of high performance organic solar cells (OSCs). Considerable efforts have been made to improve the power conversion efficiency (PCE) of oligomer-based OSCs by diverse strategies including fine-tuning of the oligomer properties via variation of their terminal and central alkyl chains, blend morphology control via solvent vapor annealing (SVA) treatment, and surface modification via interfacial engineering. These efforts allowed achieving PCEs of up to 6.4% for DTS(Oct)-(2T-DCV-Me) blended with PCBM. Further morphological investigations demonstrated that the usage of SVA treatment indeed effectively results in increased absorption and ordering of the BHJ composite, with the only exception for the most soluble oligomer DTS(Oct)-(2T-DCV-Hex). Besides, a detailed study analyzed the charge transport properties and recombination loss mechanisms for these oligomers. This study not only revealed the importance of integrated alkyl chain engineering on gaining morphological control for high performance OSCs, but also exhibited a clear correlation between molecular ordering and charge carrier mobility respective to carrier dynamics. These results outline a detailed strategy towards a rather complete characterization and optimization methodology for organic photovoltaic devices, thereby paving the way for researchers to easily find the performance parameters adapted for widespread applications.
Keywords: Engineering controlled terms: Cell engineering; Oligomers; Surface treatment; Varactors Electronwithdrawing; Morphological control; Optimization methodology; Organic photovoltaic devices; Performance parameters; Power conversion efficiencies; Solvent-vapor annealing; Structure property relationships Engineering main heading: Solar cells

Integrated System Built for Small-Molecule Semiconductors via High-Throughput Approaches - Wu, Jianchang; Zhang, Jiyun; Hu, Manman; Reiser, Patrick; Torresi, Luca; Friederich, Pascal; Lahn, Leopold; Kasian, Olga; Guldi, Dirk Michael; Perez-Ojeda Rodriguez, Maria Eugenia; Barabash, Anastasia; Rocha Ortiz, Juan Sebastian; et al. (Journal of the American Chemical Society, 2023)
High-throughput synthesis of solution-processable structurally variable small-molecule semiconductors is both an opportunity and a challenge. A large number of diverse molecules provide a possibility for quick material discovery and machine learning based on experimental data. However, the diversity of the molecular structure leads to the complexity of molecular properties, such as solubility, polarity, and crystallinity, which poses great challenges to solution processing and purification. Here, we first report an integrated system for the high-throughput synthesis, purification, and characterization of molecules with a large variety. Based on the principle “Like dissolves like,” we combine theoretical calculations and a robotic platform to accelerate the purification of those molecules. With this platform, a material library containing 125 molecules and their optical-electronic properties was built within a timeframe of weeks. More importantly, the high repeatability of recrystallization we design is a reliable approach to further upgrading and industrial production.<br

Intentional Incorporation and Tailoring of Point Defects during Sublimation Growth of Cubic Silicon Carbide by Variation of Process Parameters - Schöler, Michael; Lederer, Maximilian; Schuh, Philipp; Wellmann, Peter (physica status solidi (b), 2020)
Cubic silicon carbide (3C-SiC) is an emerging material with promising properties for various applications in power electronics, energy saving, and quantum technology. In recent years, size and quality of 3C-SiC substrates reached a level where real applications become tangible. However, there is still a lack of knowledge concerning defects in 3C-SiC. Point defects can be considered as one of the key defects, as they influence all applications in one way or another. Herein, the growth rate dependent tailoring of point defects-according to probability and density-is presented for bulk 3C-SiC grown by epitaxial sublimation growth. Photoluminescence characterization reveals a group of four distinct peaks in the near-infrared which are assumed to have their joint origin in the carbon vacancy. Moreover, indications for a novel Al-related defect are presented. The observed defects show bright luminescence in the 175 K/200 K regime and remain excitable up to 300 K.
CRIS-Team WoS Importer:2019-10-29
Keywords: cubic silicon carbide; 3C-SiC; defect engineering; point defects; sublimation growth

Intercalating-Organic-Cation-Induced Stability Bowing in Quasi-2D Metal-Halide Perovskites - Zhang, Jiyun; Langner, Stefan; Wu, Jianchang; Kupfer, Christian; Lüer, Larry; Meng, Wei; Zhao, Baolin; Liu, Chao; Daum, Manuel; Osvet, Andres; Li, Ning; Halik, Marcus; et al. (ACS Energy Letters, 2022)
Quasi-2D metal-halide perovskites with Ruddlesden-Popper structures have shown promising stability due to the protective effects of the intercalating organic cations. However, a systematic study of the effect of intercalating organic cations on stability has rarely been reported. Here we use a high-throughput-robot platform to fabricate over 300 perovskite films and study the effect of cations and their concentrations on the thermal stability of perovskite films. We find that approximately 20-25 mol % of intercalating organic cations into MAPbI3 (nominal n = 4/5) can maximize the film stability, while higher/lower concentrations lead to inferior stability, which is termed stability bowing in analogy to band-gap bowing. A model with two competitive effects of the intercalating organic cation (better protection vs more defects) is proposed to rationalize this behavior. We anticipate this work to provide new insights into the stability of quasi-2D perovskites.
CRIS-Team Scopus Importer:2022-02-11

Interface Design to Improve the Performance and Stability of Solution-Processed Small-Molecule Conventional Solar Cells - Min, Jie; Luponosov, Yuriy N.; Zhang, Zhi-Guo; Ponomarenko, Sergei A.; Ameri, Tayebeh; Li, Yongfang; Brabec, Christoph (Advanced Energy Materials, 2014)
A systematic study on the effect of various cathode buffer layers on the performance and stability of solution-processed small-molecule organic solar cells (SMOSCs) based on tris[4-[5-(1,1-dicyanobut-1-en-2-yl)-2,2-bithiophen-5-yl]phenyl]amine (N(Ph-2T-DCN-Et)3):6,6-phenyl-C71-butyric acid methyl ester (N(Ph-2T-DCN-Et)3:PC70BM) is presented. The power conversion efficiency (PCE) in these systems can be significantly improved from approximately 4% to 5.16% by inserting a metal oxide (ZnO) layer between the active layer and the Al cathode instead of an air-sensitive Ba or Ca layer. However, the low work-function Al cathode is susceptible to chemical oxidation in the atmosphere. Here, an amine group functionalized fullerene complex (DMAPA-C60) is inserted as a cathode buffer layer to successfully modify the interface towards ZnO/Ag and active layer/Ag functionality. For devices with ZnO/DMAPA-C60/Ag and DMAPA-C60/Ag cathodes the PCEs are improved from 2.75% to 4.31% and to 5.40%, respectively, compared to a ZnO/Ag device. Recombination mechanisms and stability aspects of devices with various cathodes are also investigated. The significant improvement in device performance and stability and the simplicity of fabrication by solution processing suggest this DMAPA-C60-based interface as a promising and practical pathway for developing efficient, stable, and roll-to-roll processable SMOSCs.
Keywords: Engineering controlled terms: Buffer layers; Butyric acid; Convergence of numerical methods; Conversion efficiency; Electrodes; Fullerenes; Molecules; Optical waveguides; Silver; Solar cells; Stability; Zinc oxide Cathode buffer layers; Conventional structures; Fullerene complexes; Power conversion efficiencies; Recombination mechanisms; Small-molecule organic solar cells; Solution-processing; Stability of solutions Engineering main heading: Cathodes

Interface Engineering of Perovskite Hybrid Solar Cells with Solution-Processed Perylene–Diimide Heterojunctions toward High Performance - Min, Jie; Zhang, Zhi-Guo; Hou, Yi; Ramírez Quiroz, César Omar; Przybilla, Thomas; Bronnbauer, Carina; Guo, Fei; Forberich, Karen; Azimi, Seyed Hamed; Ameri, Tayebeh; Spiecker, Erdmann; Li, Yongfang; et al. (Chemistry of Materials, 2015)
Perovskite hybrid solar cells (pero-HSCs) were demonstrated to be among the most promising candidates within the emerging photovoltaic materials with respect to their power conversion efficiency (PCE) and inexpensive fabrication. Further PCE enhancement mainly relies on minimizing the interface losses via interface engineering and the quality of the perovskite film. Here, we demonstrate that the PCEs of pero-HSCs are significantly increased to 14.0% by incorporation of a solution-processed perylene–diimide (PDINO) as cathode interface layer between the [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) layer and the top Ag electrode. Notably, for PDINO-based devices, prominent PCEs over 13% are achieved within a wide range of the PDINO thicknesses (5–24 nm). Without the PDINO layer, the best PCE of the reference PCBM/Ag device was only 10.0%. The PCBM/PDINO/Ag devices also outperformed the PCBM/ZnO/Ag devices (11.3%) with the well-established zinc oxide (ZnO) cathode interface layer. This enhanced performance is due to the formation of a highly qualitative contact between PDINO and the top Ag electrode, leading to reduced series resistance (Rs) and enhanced shunt resistance (Rsh) values. This study opens the door for the integration of a new class of easily-accessible, solution-processed high-performance interfacial materials for pero-HSCs.

Interface engineering with a novel n-type small organic molecule for efficient inverted perovskite solar cells - Wang, Helin; Yang, Fu; Li, Ning; Song, Jun; Qu, Junle; Hayase, Shuzi; Wong, Wai Yeung (Chemical Engineering Journal, 2019)
Fullerene derivatives are promising electron transporting materials for low-temperature processed inverted perovskite solar cells (PSCs). However, fullerene derivatives have some disadvantages, e.g. [6,6]-phenyl C61 butyric acid methyl ester (PCBM) has unmanageable morphology, low electron mobility and easily generated non-radiative recombination, which restrict the performance of PSCs. Herein, a novel n-type small organic molecule, homologous perylene diimide tetramer (HPDT), is designed and synthesized in this work to engineer the interface properties by enhancing interface contact, decreasing energetic barrier and recombination losses. HPDT shows suitable energy levels and high electron mobility and thus will increase the electron mobility during interface engineering in the inverted PSCs. Moreover, coating HPDT on top of perovskite prior to the deposition of PCBM is helpful to achieve a homogeneous pinhole-free PCBM layer, leading to enhanced power conversion efficiency from 17.38% up to 19.75% for inverted MAPbI3 PSCs along with a negligible hysteresis. Significantly, our results undoubtedly provide new guidelines in exploring n-type organic small molecules for high-performance PSCs.
CRIS-Team Scopus Importer:2019-12-27
Keywords: Electron transport material; Interface engineering; Perovskite solar cell; Recombination loss

Interface materials for organic solar cells - Steim, Roland; Kogler, F. Rene; Brabec, Christoph (Journal of Materials Chemistry, 2010)
The progress in the development and understanding of interfacial materials for organic photovoltaics (OPV) is reviewed. The proper choice of interface materials is a must for highly efficient and stable OPV devices and has become a significant part of the OPV research today. Interface materials are either non-conducting, semiconducting or conducting layers which not only provide selective contacts for carriers of one sort, but can also determine the polarity of OPV devices, affect the open-circuit voltage, and act as optical spacers or protective layers. In this review both inorganic and organic interface materials are discussed with respect to their function in the OPV device. © 2010 The Royal Society of Chemistry.

Interface Molecular Engineering for Laminated Monolithic Perovskite/Silicon Tandem Solar Cells with 80.4% Fill Factor - Ramírez Quiroz, César Omar; Spyropoulos, Georgios; Salvador, Michael; Roch, Loïc M.; Berlinghof, Marvin; Darío Perea, José; Forberich, Karen; Dion-Bertrand, Laura Isabelle; Schrenker, Nadine J.; Classen, Andrej; Gasparini, Nicola; Chistiakova, Ganna; et al. (Advanced Functional Materials, 2019)
A multipurpose interconnection layer based on poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS), and d-sorbitol for monolithic perovskite/silicon tandem solar cells is introduced. The interconnection of independently processed silicon and perovskite subcells is a simple add-on lamination step, alleviating common fabrication complexities of tandem devices. It is demonstrated experimentally and theoretically that PEDOT:PSS is an ideal building block for manipulating the mechanical and electrical functionality of the charge recombination layer by controlling the microstructure on the nano- and mesoscale. It is elucidated that the optimal functionality of the recombination layer relies on a gradient in the d-sorbitol dopant distribution that modulates the orientation of PEDOT across the PEDOT:PSS film. Using this modified PEDOT:PSS composite, a monolithic two-terminal perovskite/silicon tandem solar cell with a steady-state efficiency of 21.0%, a fill factor of 80.4%, and negligible open circuit voltage losses compared to single-junction devices is shown. The versatility of this approach is further validated by presenting a laminated two-terminal monolithic perovskite/organic tandem solar cell with 11.7% power conversion efficiency. It is envisioned that this lamination concept can be applied for the pairing of multiple photovoltaic and other thin film technologies, creating a universal platform that facilitates mass production of tandem devices with high efficiency.
Keywords: density functional theory; lamination; molecular dynamics; monolithic tandem; perovskite/silicon; transparent-conductive-adhesive

Intermetallic compounds dynamic formation during annealing of stacked elemental layers and its influences on the crystallization of Cu2ZnSnSe4 films - Wibowo, Rachmat Adhi; Möckel, Stefan; Yoo, Hye Sun; Hetzner, Christina; Hölzing, Astrid; Wellmann, Peter; Hock, Rainer (Materials Chemistry and Physics, 2013)
A combined in-situ investigation using X-ray diffraction and differential scanning calorimetry during annealing was carried out to investigate the formation of intermetallic compounds in the stacked elemental layers and to reveal its influences on the crystallization of kesterite Cu2ZnSnSe4. The Mo/Cu/Zn, Mo/Cu/Sn/Zn, Mo/Cu/Zn/Se and Mo/Cu/Sn/Zn/Se stacked films were prepared with a composition resembling a typical kesterite Cu-poor and Zn-rich metallic composition. In-situ experiments during annealing of pure metallic stacked films reveal a dynamic intermetallic compounds formation of Cu5Zn8 -> CuZn -> Cu2Zn -> Cu3Zn and Cu6Sn5 -> Cu41Sn11. The Cu-Zn and Cu5Zn8 layer formed at the interface of metals/Se may prevent the stacked metallic layers from selenization below 320 degrees C. On the other side, the dynamic formation of Cu-Zn phases in the stacked films is found to be an origin of a ZnSe gradual formation starting from 320 degrees C. Phase analysis suggests that the ternary Cu2SnSe3 phase forms almost immediately after the formation of Cu2Se and SnSe. The formation of Cu2SnSe3 is indicated by the consumption of SnSe by the Cu2Se which occurs at 530-540 degrees C. Crystallization of kesterite takes place above 540 degrees C. On a phenomenological basis of present results, consequences for the thin film kesterite fabrication for solar cell application are discussed. (C) 2013 Elsevier B.V. All rights reserved.
Keywords: Intermetallic compounds; Thin films; Annealing; Sputtering; Differential scanning calorimetry (DSC)

Interplay between the magnetic and transport properties in the III-V diluted magnetic semiconductor Ga1-xMnxAs - Van Esch, A.; Van Bockstal, L.; De Boeck, J.; Verbanck, G.; Van Steenbergen, A.S.; Wellmann, Peter; Grietens, B.; Bogaerts, R.; Herlach, F.; Borghs, G. (Physical Review B, 1997)
Using a low-temperature molecular-beam epitaxy growth procedure, Ga1-xMnxAs-a III-V diluted magnetic semiconductor-is obtained with Mn concentrations up to x similar to 9%. At a critical temperature T-c (T-c approximate to 50 K for x=0.03-0.05), a paramagnetic to ferromagnetic phase transition occurs as the result of the interaction between Mn-h complexes. Hole transport in these compounds is strongly affected by the antiferromagnetic exchange interaction between holes and Mn 3d spins. A model for the transport behavior both above and below Tc( )is given. Above T-c, all materials exhibit transport behavior which is characteristic for systems near the metal-insulator transition. Below T-c, due to the rising spontaneous magnetization, spin-disorder scattering decreases and the relative position of the Fermi level towards the mobility edge changes. When the magnetization has reached its saturation value (below similar to 10 K) variable-range hopping is the main conduction mechanism. The negative magnetoresistance is the result of the expansion of the hole wave functions in an applied magnetic field.

Intrinsically Activated SrTiO3: Photocatalytic H2 Evolution from Neutral Aqueous Methanol Solution in the Absence of Any Noble Metal Cocatalyst - Zhou, Xuemei; Liu, Ning; Yokosawa, Tadahiro; Osvet, Andres; Miehlich, Matthias; Meyer, Karsten; Spiecker, Erdmann; Schmuki, Patrik (ACS Applied Materials and Interfaces, 2018)
Noble metal cocatalysts are conventionally a crucial factor in oxide-semiconductor-based photocatalytic hydrogen generation. In the present work, we show that optimized high-temperature hydrogenation of commercially available strontium titanate (SrTiO3) powder can be used to engineer an intrinsic cocatalytic shell around nanoparticles that can create a photocatalyst that is highly effective without the use of any additional cocatalyst for hydrogen generation from neutral aqueous methanol solutions. This intrinsic activation effect can also be observed for SrTiO3[100] single crystal as well as Nb-doped SrTiO3[100] single crystal. For all types of SrTiO3 samples (nanopowders and either of the single crystals), hydrogenation under optimum conditions leads to a surface-hydroxylated layer together with lattice defects visible by transmission electron microscopy, electron paramagnetic resonance (EPR), and photoluminescence (PL). Active samples provide specific defects identified by EPR, PL, and electron-energy loss spectroscopy as Ti3+ states in a defective matrix—this is in contrast to the inactive defects formed in other reductive atmospheres. In aqueous media, active SrTiO3 samples show a significant negative shift of the flatband potential (in photoelectrochemical as well as in capacitance data) and a lower charge-transfer resistance for photoexcited electrons. We therefore ascribe the remarkable cocatalyst-free activation of the material to a synergy between thermodynamics (altered interface energetics induced by hydroxylation) and kinetics (charge transfer mediation by suitable Ti3+ states
Keywords: water splitting; noble-metal-free; SrTiO3; intrinsic activation; hydrogenation

Intrinsically Activated SrTiO3: Photocatalytic H2 Evolution from Neutral Aqueous Methanol Solution in the Absence of Any Noble-Metal Co-catalyst - Zhou, Xuemei; Liu, Ning; Yokosawa, Tadahiro; Osvet, Andres; Miehlich, Matthias; Meyer, Karsten; Spiecker, Erdmann; Schmuki, Patrik (ACS Applied Materials and Interfaces, 2018)
Noble metal cocatalysts are conventionally a crucial factor in oxide-semiconductor-based photocatalytic hydrogen generation. In the present work, we show that optimized high-temperature hydrogenation of commercially available strontium titanate (SrTiO3) powder can be used to engineer an intrinsic cocatalytic shell around nanoparticles that can create a photocatalyst that is highly effective without the use of any additional cocatalyst for hydrogen generation from neutral aqueous methanol solutions. This intrinsic activation effect can also be observed for SrTiO3[100] single crystal as well as Nb-doped SrTiO3[100] single crystal. For all types of SrTiO3 samples (nanopowders and either of the single crystals), hydrogenation under optimum conditions leads to a surface-hydroxylated layer together with lattice defects visible by transmission electron microscopy, electron paramagnetic resonance (EPR), and photoluminescence (PL). Active samples provide specific defects identified by EPR, PL, and electron-energy loss spectroscopy as Ti3+ states in a defective matrix-this is in contrast to the inactive defects formed in other reductive atmospheres. In aqueous media, active SrTiO3 samples show a significant negative shift of the flatband potential (in photoelectrochemical as well as in capacitance data) and a lower charge-transfer resistance for photoexcited electrons. We therefore ascribe the remarkable cocatalyst-free activation of the material to a synergy between thermodynamics (altered interface energetics induced by hydroxylation) and kinetics (charge transfer mediation by suitable Ti3+ states
Keywords: SrTiO3; hydrogenation; intrinsic activation; noble-metal-free; water splitting

Introducing a New Potential Figure of Merit for Evaluating Microstructure Stability in Photovoltaic Polymer-Fullerene Blends - Perea, Jose Dario; Langner, Stefan; Salvador, Michael Filipe; Sanchez-Lengeling, Benjamin; Li, Ning; Zhang, Chaohong; Jarvas, Gabor; Kontos, Janos; Dallos, Andras; Aspuru-Guzik, Alan; Brabec, Christoph (Journal of Physical Chemistry C, 2017)
A theoretical understanding of the microstructure of organic semiconducting polymers and blends is vital to further advance the optoelectronic device performance of organic electronics. We outline the theoretical framework of a combined numerical approach based on polymeric solution theory to study the microstructure of polymer:small molecule blends. We feed the results of ab initio density functional theory quantum chemistry calculations into an artificial neural network for the determination of solubility parameters. These solubility parameters are used to calculate Flory-Huggings intermolecular parameters. We further show that the theoretical values are in line with experimentally determined data. On the basis of the Flory-Huggings parameters, we establish a figure of merit as a relative metric for assessing the phase diagrams of organic semiconducting blends in thin films. This is demonstrated for polymer:fullerene blend films on the basis of the prototypical polymers poly(3-hexylthiophene-2,5-diyl) (P3HT) and poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3-di(2-octyldodecyl)-2,2,5,2;5,2-quaterthiophen-5,5-diyl)] (PffBT4T-2OD). After confirming the applicability of our model with a broader range of materials and differences in molecular weight, we suggest that this combined model should be able to inform design criteria and processing guidelines for existing and new high performance semiconducting blends for organic electronics applications with ideal and stable solid state morphology. (Graph Presented). © 2017 American Chemical Society.
Keywords: BlendingCalculationsDensity functional theoryFullerenesMicrostructureNeural networksOptoelectronic devicesOrganic polymersPolymer filmsPolymersQuantum chemistrySemiconducting filmsSemiconducting polymersSolubility

Introducing a new triazoloquinoxaline-based fluorene copolymer for organic photovoltaics: Synthesis, characterization, and photovoltaic properties - Baran, Derya; Pasker, Felix M.; Le Blanc, Stephan; Schnakenburg, Gregor; Ameri, Tayebeh; Hoeger, Sigurd; Brabec, Christoph (Journal of Polymer Science Part A-Polymer Chemistry, 2013)
A new donor-acceptor copolymer consisting of triazoloquinoxaline and 9,9-dialkylfluorene units on the main chain has been synthesized, characterized and evaluated as donor material in bulk heterojunction solar cells using PC BM as an acceptor. The resulting polymer PTQF showed good thermal stability and solubility in common organic solvents. Cyclic Voltammetry measurements showed that the PTQF has HOMO-LUMO energy levels of -5.13 and -3.62 eV, respectively. DFT calculations revealed that the HOMO is delocalized all over the thiophene and fluorene units and the LUMO is localized mainly on the triazole and pyrazine units. PTQF absorbs broadly in the visible region and exhibits a bandgap of 1.4 eV. Photovoltaic devices exhibited 1.7% efficiency for 1:2 PTQF:PCBM blend ratio using Ca/Ag electrodes. © 2012 Wiley Periodicals, Inc.
Keywords: benzotriazole; conducting polymers; conjugated polymers; electrochemistry; fluorene copolymer; organic photovoltaics; Suzuki coupling; triazoloquinoxaline

Introduction - Kafafi, Zakya H.; Brabec, Christoph; Lane, Paul A. (Proceedings of SPIE - The International Society for Optical Engineering, 2012)

Inverse design workflow discovers hole-transport materials tailored for perovskite solar cells - Wu, Jianchang; Torresi, Luca; Hu, Manman; Reiser, Patrick; Zhang, Jiyun; Rocha-Ortiz, Juan S.; Wang, Luyao; Xie, Zhiqiang; Zhang, Kaicheng; Park, Byung-Wook; Barabash, Anastasia; Zhao, Yicheng; et al. (Science, 2024)
The inverse design of tailored organic molecules for specific optoelectronic devices of high complexity holds an enormous potential but has not yet been realized. Current models rely on large data sets that generally do not exist for specialized research fields. We demonstrate a closed-loop workflow that combines high-throughput synthesis of organic semiconductors to create large datasets and Bayesian optimization to discover new hole-transporting materials with tailored properties for solar cell applications. The predictive models were based on molecular descriptors that allowed us to link the structure of these materials to their performance. A series of high-performance molecules were identified from minimal suggestions and achieved up to 26.2% (certified 25.9%) power conversion efficiency in perovskite solar cell
CRIS-Team Scopus Importer:2025-02-04

Inverted, Environmentally Stable Perovskite Solar Cell with a Novel Low-Cost and Water-Free PEDOT Hole-Extraction Layer - Hou, Yi; Zhang, Hong; Chen, Wei; Chen, Shi; Ramírez Quiroz, César Omar; Azimi, Seyed Hamed; Osvet, Andres; Matt, Gebhard; Zeira, Eitan; Seuring, Jan; Kausch-Busies, Nina; Loevenich, Wilfried; et al. (Advanced Energy Materials, 2015)
A power conversion efficiency of 11.8% is demonstrated for planar perovskite solar cell based on acid water-free poly(3,4-ethylenedioxythiophene) (PEDOT) as the hole-transporting layer. This efficiency is further improved to 14.2% using a pH neutralized PEDOT, which reduces the sub-gap defects at the surface of perovskite. All the active layers reported are solution-processed at temperatures below 140 °C making it compatible with roll-to-roll production.
Keywords: low-temperature processing; perovskite solar cells; stabilities; water-free poly(3; 4-ethylenedioxythiophene)

Inverted organic solar cells using a solution processed aluminum-doped zinc oxide buffer layer - Stubhan, Tobias; Oh, Hyunchul; Pinna, Luigi; Krantz, Johannes; Litzov, Ivan; Brabec, Christoph (Organic Electronics, 2011)
In this article, we demonstrate a route to solve one of the big challenges in the large scale printing process of organic solar cells, which is the reliable deposition of very thin layers. Especially materials for electron (EIL) and hole injection layers (HIL) (except poly(3,4-ethylene dioxythiophene): (polystyrene sulfonic acid) (PEDOT:PSS)) have a low conductivity and therefore require thin films with only a few tens of nanometers thickness to keep the serial resistance under control. To overcome this limitation, we investigated inverted polymer solar cells with an active layer comprising a blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C-butyric acid methyl ester (PCBM) with solution processed aluminum-doped zinc oxide (AZO) EIL. Devices with AZO and intrinsic zinc oxide (i-ZnO) EIL show comparable efficiency at low layer thicknesses of around 30 nm. The conductivity of the doped zinc oxide is found to be three orders of magnitude higher than for the i-ZnO reference. Therefore the buffer layer thickness can be enhanced significantly to more than 100 nm without hampering the solar cell performance, while devices with 100 nm i-ZnO films already suffer from increased series resistance and reduced efficiency. © 2011 Elsevier B.V. All rights reserved.
Keywords: Al doped ZnO; Electron injection layer; Inverted structure; Polymer solar cell; Solution processing; Zinc oxide nanoparticles

Inverted structure organic photovoltaic devices employing a low temperature solution processed WO 3 anode buffer layer - Li, Ning; Stubhan, Tobias; Luechinger, Norman A.; Halim, Samuel C.; Matt, Gebhard; Ameri, Tayebeh; Brabec, Christoph (Organic Electronics, 2012)
Solution processing is a convenient method and also the guarantee for low cost and large-scale organic photovoltaic (OPV) production. It was recently suggested that the absorption of OPV devices can be spectrally extended by introducing ternary semiconductor blends, where a second donor with a complementary absorption spectrum is added into the active layer. In this manuscript we demonstrate the successful replacement of poly(3,4- ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) by low temperature solution processed tungsten trioxide (WO ) nanoparticles for inverted OPV devices based on either poly(3-hexylthiophene) (P3HT): phenyl-C61-butyric acid methyl ester (PCBM) or P3HT: poly[2,1,3-benzothiadiazole-4,7-diyl[4,4- bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b′]dithiophene-2,6-diyl]] (Si-PCPDTBT):PCBM active layers. These WO nanoparticles can serve as fully functional anode buffer layers in inverted OPV devices without further treatment, while showing comparable functionality as PEDOT:PSS layers. © 2012 Elsevier B.V. All rights reserved.
Keywords: Anode buffer layer; Inverted structure; Organic photovoltaic; Solution processing; WO 3 nanoparticles

Investigating and Improving Performance Ratio of Cu(In,Ga)(S,Se)2 Photovoltaic Devices - Weber, Alfons; Lechner, Robert; Grünsteidl, Stefan; Borowski, Peter; Schubbert, Christian; Dalibor, Thomas; Heise, Stephan J.; Ohland, Joerg; Savchenko, Iievgeniia; Ahmed, Hamsa; Hirwa, Hippolyte; Parisi, Juergen; et al. (EU PVSEC, 2020)
For a commercial photovoltaic product not only the efficiency under standard test conditions (1000 W/m², AM1.5, Tcell=25°C) but also the performance under different operating conditions in the field is of importance. In this contribution, first results and the current status of a new project for Yield maximized Cu(In,Ga)(S,Se)2 thin film solar modules by deliberately controlled parameters of performance ratio (MyCIGS)2 are presented. In a comprehensive approach MyCIGS covers the combination of material and process variations in the different device layers, material characterisation of these layers, opto-electrical characterisation of the resulting devices, device and performance simulation and finally outdoor module testing to identify and optimize the key contributors for the performance ratio. With Avancis and the Helmholtz-Zentrum Berlin, the MyCIGS project comprises two partners that can supply completely processed cell or module samples or the single layers starting from the back electrode and thus allowing for a large field of possible process and material variations. Material characterisation is done by all project partners with a focus at the University of Erlangen on absorber characterisation via X-ray diffraction, scanning electron microscopy and photoluminescence. With the various characterisation techniques the absorber composition and its grading with absorber thickness, quality of module patterning, optical properties and electrical properties of the complete device are investigated. Material and device characterisation are the basis for a TCAD3 device model by the University of Oldenburg to also allow for a simulation-based approach to optimise the different contributors to performance ratio. The impact of the tested process variations on the parameters of performance ratio is tested indoor and also outdoor on two newly installed field test setups in Munich and Berlin. In a first experimental series, various process parameters have been investigated: composition of the back electrode, composition of the absorber (Ga-poor and S-poor versus Ga-rich and S-rich), buffer material and ilayer. In this contribution we will show the results of the absorber variation in more detai
Keywords: solar cells; CIGSe; characterization; outdoor test; performance

Investigation of amorphous-SiC thin film deposition by RF magnetron sputtering for optical applications - Chaussende, Didier; Tabouret, Vincent; Crisci, Alexandre; Morais, Magali; Coindeau, Stéphane; Berthomé, Gregory; Kollmuß, Manuel; Wellmann, Peter; Jomard, François; Pinault-Thaury, Marie Amandine; Lu, Yaoqin; Shi, Xiaodong; et al. (Materials Science in Semiconductor Processing, 2024)
Silicon carbide (SiC) is a rapidly emerging material for photonic applications, thanks to its exceptional optical properties. To be used as a waveguide, SiC thin films must be deposited directly on silica at low temperature. Amorphous SiC films were deposited by RF magnetron sputtering using a single source of high-purity polycrystalline SiC. A systematic study of the chemical, structural and optical properties of the films was carried out, using a combination of XRD, XPS, SIMS, spectroscopic ellipsometry, Raman spectroscopy and UV–Vis absorption spectroscopy. The aim was to link deposition conditions to film properties. By exploring a three-parameter space (RF power, substrate temperature, pressure), we have demonstrated that RF power is the main parameter which controls the entire deposition process and film properties. By simply adjusting the RF plasma power between 150 and 450 W, it is possible to adjust the refractive index at a wavelength of 1.5 μm in the range 2.50–2.75 and vary the bandgap from 2.5 to 1.7 eV. This is attributed to a slight variation in film composition, particularly in terms of Si/C ratio and C–C bond concentration.
CRIS-Team Scopus Importer:2024-07-19
Keywords: Amorphous; Deposition process; Magnetron sputtering; Optical properties; Silicon carbide

Investigation of a PVT SiC-growth set-up modified by an additional gas flow - Straubinger, Thomas; Wellmann, Peter; Winnacker, Albrecht (Materials Science Forum, 2001)
We have investigated a new type of a so called "modified PVT setup" with an additional gas flow into the growth cell. The motivation was an improvement of the parameter control for doping of SiC using gas sources, i.e. homogenization of doping levels. Since an additional gas flow inside the growth cell could cause severe distortions of the vapor flow we have performed basic investigations of the influence of an inner argon gas stream on thermal field and structural properties of the growing crystal. We have studied the impact of the extern gas flow towards the surface of the growing crystal. Strong evidence for micropipe closing in the initial growth stage and reduction of second phase inclusions was foun
Keywords: Doping; Inclusion; Micropipe Closing; Modified-PVT

Investigation of deep electronic levels in n‐type and p‐type 3C‐SiC using photoluminescence - Wilhelm, Martin; Syväjärvi, Mikael; Wellmann, Peter (Advanced Materials Proceedings, 2017)
Among the various SiC polytypes, cubic 3C‐SiC is much more difficult to grow in high crystalline quality than the commercially introduced hexagonal 6H‐SiC and 4H‐SiC counterparts. Besides some benefits of 3C‐SiC for transistor applications related to a greater electron mobility and a lower metal‐oxide‐semiconductor interface trap density compared to 4H‐SiC, new potential optoelectronic applications have been introduced very recently. Boron doped 3C‐SiC may act as an ideal candidate for an intermediate band (IB) solar cell material. Aluminum doped p‐type 3C‐SiC could lead to the development of efficient optoelectrochemical water splitting cells. Finally, 3C‐SiC with its various intrinsic point defects has been considered as a suitable candidate for future spintronic‐applications. All these applications will critically depend on further understanding defect behaviour on atomic level. In our study we investigated free standing n‐type and p‐type 3C‐SiC material grown in our lab. Temperature dependent photoluminescence measurements revealed the presence of carbon vacancy related VC and VC-CSi defect transitions in the p‐type materials but not in the n‐type materials. This observation present in as grown 3C-SiC is believed to have significant impact on the optoelectronic applications.
Keywords: 3C-SiC; doping; p-type; defects; carbon vacancy

Investigation of defects in 4H-SiC and the SiC/SiO2 interface using DLTS measurements - Xue, Weidong (Friedrich-Alexander-Universität Erlangen-Nürnberg, 2023)
Devices based on 4H-SiC have not only played a significant role in power electronics but have also shown remarkable potential in quantum applications. Currently, these devices are demonstrating astonishing capabilities in the field of quantum technology. Silicon vacancies located within 4H-SiC, for instance, can effectively serve as efficient quantum dots. However, it cannot be ignored that other types of defects present in 4H-SiC also impact silicon vacancies. For instance, the presence of fixed charges in the vicinity of the silicon vacancies can lead to the broadening of the excitation spectrum. Additionally, the emission wavelength can fluctuate over time due to mobile charges, thereby constraining the further development of quantum applications. In this master's thesis, an in-depth exploration of the defect landscape in 4H-SiC-based devices is investigated using the powerful technique of deep-level transient spectroscopy (DLTS). By characterizing the defects under different processing conditions, their behaviour and impact on device performance could be uncovered. Epitaxial 4H-SiC layers will be used to fabricate a range of devices, including MOS capacitors prepared using diverse oxidation processes such as plasma-enhanced chemical vapor deposition (PECVD), low-pressure chemical vapor deposition (LPCVD), and various thermal oxidation methods. Additionally, Schottky capacitors will be fabricated based on dry thermal oxidation MOS capacitor to comprehensively investigate the defect landscape. Before conducting the DLTS experiments, certain electrical connection issues about the series resistance of chuck and natural oxide of polysilicon were also addressed. This was primarily achieved by ensuring the closeness of the two spots of silver glue and employing Focused Ion Beam (FIB) with Platinum deposition. This successful approach resulted in the alignment of the C-V curves obtained from DLTS with those obtained from standard C-V experiments. During DLTS measurements, new defect levels ON1 and ON2 originated from excess carbon are found to be introduced through thermal oxidation, along with the observation of silicon vacancies. Similar new defects were observed in LPCVD MOS capacitors, resembling those introduced during thermal oxidation, but they are most probably not the same defects because there will be no excess carbon in LPCVD process, so they are suspectable to be some intrinsic defects or caused by some residuals from LPCVD process. Additionally, various defects were identified in the Schottky diode capacitors including silicon vacancy. Furthermore, high-dose and low-dose electron irradiation will also be utilized. After electron irradiation, an increase in the concentration of defects related to carbon vacancies in the Schottky diode capacitors can be observed. However, this phenomenon has not been observed in the MOS capacitor

Investigation of mass transport during PVT growth of SiC by 13C labeling of source material - Herro, Ziad Georges; Wellmann, Peter; Püsche, Roland; Hundhausen, Martin; Ley, Lothar; Maier, Matthias; Masri, P.; Winnacker, Albrecht (Journal of Crystal Growth, 2003)
We have investigated experimentally mass transport during physical vapor transport growth of silicon carbide (SiC). 13C was used as trace in order to determine mass transport paths inside the SiC source material as well as inside the gas room. The 13C concentration inside the SiC crystal, SiC source material and parts of the graphite growth cell was measured using micro-Raman spectroscopy and secondary ion mass spectroscopy. The SiC growth process was monitored using digital X-ray imaging. The presented method for the first time provides experimental access to mass transport which is of particular interest (i) for fundamental investigations, and (ii) for the verification of numerical modeling tools which are currently widely in use for the improvement of the SiC growth proces
Keywords: Growth from vapor; Mass transfer; Si13C

Investigation of mass transport during SiCPVT growth using digital X-ray imaging, C-13 labeling of source material and numerical modeling - Wellmann, Peter; Herro, Ziad Georges; Selder, Markus; Durst, F.; Püsche, Roland; Hundhausen, Martin; Ley, Lothar; Winnacker, Albrecht (Materials Science Forum, 2003)
We have analyzed the mass transport during physical vapor transport growth of SiC using C-13 for labeling of the SiC gas species (i.e. Si2C and SiC2) paths and digital x-ray imaging in order to monitor the evolution of the SiC crystal and SiC source material. The distribution of (SiC)-C-13 was investigated after growth by Micro-Raman spectroscopy. The slow onset of the C-13 incorporation into the SiC crystal as well as the enrichment of C-13 in the residual source material indicate that the major mass transport is conducted through the center of the source material and not along the hot crucible walls where SiC consumption is observed first. Numerical modeling of sublimation and recrystallization inside the SiC source material has been carried out. Effects like the formation of a condensed disk on top of the source material, consumption of SiC close to the hot crucible walls, etc. are described well. The experimental as well as numerical methods are believed to be useful tools for scaling up current growth setups towards large single crystal diameter
Keywords: Physical Vapor Transport Growth; Raman Spectroscopy; Si13C; Source Material; X-Ray Imaging

Investigation of the beta'- to alpha-phase transformation temperature of (Ca1-xMgx)3(PO4)2 solid solutions - Götz-Neunhoeffer, Friedlinde; Neubauer, Jürgen; Enderle, Ralph; Göbbels, Matthias (Zeitschrift für Kristallographie, Supplement, 2007)
Tricalcium phosphate Ca3(PO4)2 (TCP), an osteoconductive as well as bioresorbable phase, has found application as bone cement and bone implant material. TCP was found to crystallize in three polymorphic modifications: β-TCP below 1180°C, α-TCP between 1180°C and 1430°C, and α-TCP above 1430°C [1]. It is mainly β-TCP and α-TCP that have gained acceptance in biomedical applications. At the moment β-TCP ceramics are used for non-load-bearing applications in oral surgery. In this investigation we were able to detect an additional but reversible phase transformation from β- to β′-TCP at 1000°C. The influence of partial Mg2+ substitution of Ca 2+ in the solid solution series of β′-TCP (Ca 1-xMgx)3(PO4)2 was determined at 1025°C ± 10°C in air. The temperatures for β′- to α-TCP phase transformation were investigated in a manner differentiated according to the different Mg2+ contents.
UnivIS-Import:2015-03-09:Pub.2007.nat.dgeo.IGM.LM.invest
Keywords: Polymorphic modifications; Rietveld refinement; Solid solution; Tricalcium phosphate (TCP); X-ray powder diffraction

Investigation of the charge carrier concentration in highly aluminum doped SiC using Raman scattering - Müller, Ralf; Künecke, Ulrike; Thuaire, A.; Mermoux, M.; Pons, Michel; Wellmann, Peter (Physica Status Solidi C: Conferences, 2006)
in the production of highly aluminum doped SiC bulk crystals, a need arises for a fast and simple method to estimate the hole concentration in the material for process control and optimization. An approach for a characterization method using Raman spectroscopy is presented. We established a calibration curve along with an empirical function to determine the charge carrier concentration in p-type SiC from the line width of a linear optical phonon - plasmon coupled (LOPC) mode. At charge carrier concentrations below 10(18) cm(-3), a good precision with a relative error of 10 to 15 % for the hole concentration can be obtained. At charge carrier concentrations of p > 10(19) cm(-3), the relative error rises to 50 % for p because of the low signal/noise ratio in the LOPC spectra. (c) 2006 WILEY-VCH Verlag GmbH & Co KGaA, Weinhei
Keywords: Silicon Carbide; charge carrier concentration; Al-doped; Raman

Investigation of the growth kinetics of SiC crystals during physical vapor transport growth by the application of in-situ 3D computed tomography visualization - Arzig, Matthias; Salamon, Michael; Uhlmann, Norman; Wellmann, Peter (Advanced Engineering Materials, 2019)
Computed tomography using X‐rays has been applied during bulk growth of SiC in order to investigate growth kinetics in‐situ during the physical vapor transport process. Besides the standard SiC source material, in particular a pure solid source SiC block is used. It is found that the growth rate is lowered as the sublimation of gaseous species is limited to the top part of the solid source. The morphological changes in the source area during growth differ significantly compared to the process when conventional powder is used. The formation of multiple growth centers on the surface of the seed is monitored in‐situ with a computed tomography system. In a series of experiments the influence of the supersaturation on the growth is examined. The in‐situ computed tomography shows that the curvature of the growth interface is stronger influenced by the thermal field at higher pressures. A high supersaturation leads to the formation of rather smooth surface morphologies while the formation of large steps on the surface was induced at lower supersaturation
Keywords: SiC; solid source; supersaturation; in-situ CT; facet

Investigation of the Nucleation Process During the Initial Stage of PVT Growth of 4H-SiC - Strüber, Sven; Arzig, Matthias; Steiner, Johannes; Salamon, Michael; Uhlmann, Norman; Wellmann, Peter (Solid State Phenomena, 2023)
Due to high growth temperatures during the physical vapor transport (PVT) it is still almost impossible to gain proper insight into the actual growth conditions. Therefore, computer tomography (CT) is used as an in-situ monitoring during the crystal growth process. With the help of this technique, it is possible to observe the nucleation centers during the initial stage of growth (CT after 0 h) of a 4H-SiC single crystal. These growth islands are likely formed before the actual growth conditions are reached. Raman investigations of the area around a growth island located directly on the interface between seed and grown crystal is used to support this assumption. In addition, optical analysis after KOH etching were made to reveal the defects around the growth island. The island exhibits a inhomogeneous doping concentration in comparison to the surrounding grown crystal.
CRIS-Team Scopus Importer:2023-06-23
Keywords: 4H-SiC; initial stage; nucleation; PVT; Raman; X-ray in-situ visualization (CT)

Investigation of the ß-alpha TCP phase transformation in dependence of Mg-content - Götz-Neunhoeffer, Friedlinde; Göbbels, Matthias; Enderle, Ralph (Proc. of the 19th General Meeting of the IMA, 2006)
UnivIS-Import:2015-04-16:Pub.2006.nat.dgeo.IGM.LM.invest

Iodide-capped PbS Quantum dots: Full optical characterization of a versatile absorber - Stadler, Philipp; Mohamed, Shaimaa A.; Gasiorowski, Jacek; Sytnyk, Mykhailo; Yakunin, Sergii; Scharber, Markus C.; Enengl, Christina; Enengl, Sandra; Egbe, Daniel A. M.; El-Mansy, Mabrouk K.; Obayya, Salah S. A.; Sariciftci, N. Serdar; et al. (Advanced Materials, 2015)
(Graph Presented) Lead sulfide quantum dots represent an emerging photovoltaic absorber material. While their associated optical qualities are true for the colloidal solution phase, they change upon processing into thin-films. A detailed view to the optical key-parameters during solid-film development is presented and the limits and outlooks for this versatile and promising absorber are discussed.
Keywords: Atomic ligands; Lead sulfide quantum dots; Quantum dot photovoltaic cells; Spectroscopic ellipsometry; Time-resolved photoluminescence

Ionic Charging by Local Imbalance at Interfaces in Hybrid Lead Halide Perovskites - Almora Rodriguez, Osbel; Guerrero, Antonio; Garcia-Belmonte, Germà (Applied Physics Letters, 2016)
When mixed ionic-electronic conductors are used in optoelectronic devices. Ionic effects in perovskitesolar cells are believed to be distorted. Current hysteresis and switchable photovoltaic characteristics have been linked to the kinetics of ion migration. However, the nature of the specific ionic mechanism (or mechanisms) can not be understood. It is considered that the local rearrangement of the electrode interfaces gives rise to a high degree of apparent capacitive effects. CH3NH3PbI3 samples show two main polarization processes and reveal the structure of the ionic double-layer at the interface with the non-reacting contacts. It is observed that the ionic charging, with a typical response time of 10 seconds, is a local effect confined in the vicinity of the electrode, which entails absence of net mobile ionic concentration (space-charge) in the material bulk.<br
Keywords: organic compounds; ionic conductivity; lead compounds

Ionic Dipolar Switching Hinders Charge Collection in Perovskite Solar Cells with Normal and Inverted Hysteresis - Almora Rodriguez, Osbel; Lopez-varo, Pilar; Cho, Kyung Taek; Aghazada, Sadig; Meng, Wei; Hou, Yi; Echeverria-Arrondo, Carlos; Zimmermann, Iwan; Matt, Gebhard; Jiménez-Tejada, Juan A.; Brabec, Christoph; Nazeeruddin, Mohammad Khaja; et al. (Solar Energy Materials and Solar Cells, 2019)
Drift-diffusion modeling of the ionic dipole switching from the measurement of fast scanned and long pre-biased electrical response is proposed as a novel protocol for evaluation of limit hysteretic effects in perovskite solar cells. Up to eight systems were measured including CH3NH3PbI3, Cs0.1FA0.74MA0.13PbI2.48Br0.39 and FA0.83MA0.17Pb1.1Br0.22I2.98 3D perovskite absorbers, as well as 2D capping layers towards the selective contacts. We show systematic hysteretic patterns, even among typical hysteresis-free devices, including normal and inverted hysteresis as general dissimilar trend between CH3NH3PbI3 and mixed perovskite cells, respectively. Particularly, strong changes in the short-circuit current density (Jsc) were identified, in addition to different trends affecting the fill factor (FF) and the open-circuit voltage (Voc). The changes in Jsc were analyzed with state-of-the-art numerical drift-diffusion simulations concluding in an important reduction in the charge collection due to ionic distribution switching depending on the pre-biasing protocol and the type of absorbing perovskite. It is shown that mixed perovskites inhibit ionic dipolar switching. In addition, our calculi signal on the required conditions for the occurrence of inverted hysteresis and changes in the Voc. Regarding the FF and Voc patterns a new empirical approach is introduced and corresponding interpretations are proposed. <br
Keywords: Perovskite solar cells; Ionic polarization; Hysteresis; Photocurrent

Ion-induced field screening as a dominant factor in perovskite solar cell operational stability - Thiesbrummel, Jarla; Shah, Sahil; Gutierrez-Partida, Emilio; Zu, Fengshuo; Peña-Camargo, Francisco; Zeiske, Stefan; Diekmann, Jonas; Ye, Fangyuan; Peters, Karol P.; Brinkmann, Kai O.; Caprioglio, Pietro; Dasgupta, Akash; et al. (Nature Energy, 2024)
The presence of mobile ions in metal halide perovskites has been shown to adversely affect the intrinsic stability of perovskite solar cells (PSCs). However, the actual contribution of mobile ions to the total degradation loss compared with other factors such as trap-assisted recombination remains poorly understood. Here we reveal that mobile ion-induced internal field screening is the dominant factor in the degradation of PSCs under operational conditions. The increased field screening leads to a decrease in the steady-state efficiency, often owing to a large reduction in the current density. Instead, the efficiency at high scan speeds (>1,000 V s−1), where the ions are immobilized, is much less affected. We also show that the bulk and interface quality do not degrade upon ageing, yet the open-circuit voltage decreases owing to an increase in the mobile ion density. This work reveals the importance of ionic losses for intrinsic PSC degradation before chemical or extrinsic mechanical effects manifest.
CRIS-Team Scopus Importer:2024-04-05

Ion-mediated hopping electrode polarization model for impedance spectra of CH3NH3PbI3 - Almora Rodriguez, Osbel; González-Lezcano, Alfredo; Guerrero, Antonio; Brabec, Christoph J.; Garcia-Belmonte, Germa (Journal of Applied Physics, 2020)
Methylammonium lead iodide (CH3NH3PbI3) is one of the most attractive materials for optoelectronic applications, and it is the most typical absorber in perovskite solar cells, which are unprecedentedly successful devices in terms of power conversion efficiency. In this work, the conductivity and capacitance spectra of symmetrically contacted Au/CH3NH3PbI3/Au thick pellets are measured via impedance spectroscopy at different temperatures in dark equilibrium. The experimental conductivity spectra are parameterized and showed to follow the formalism of hopping DC conductivity in the CH3NH3PbI3 bulk. The presence of several regimes for the general Jonscher's “universal” conductivity–frequency response is highlighted and associated with the ionic–electronic overlapping conductivities. For the capacitance spectra, the general features of electrode polarization capacitance at the CH3NH3PbI3/Au interfaces are identified but yet are found to be in disagreement with some trends of classical ionic conductivity models, unable to separate different contributions. Accordingly, an analytical model is proposed accounting for hopping processes where the low frequency activation energy is split into ionic and electronic components. Our parameterizations and analytical model discern between the bulk/interface and ionic/electronic phenomena and estimate the multiple activation energies in this hybrid halide perovskite.<br
Keywords: Electrodes; Photovoltaics; Perovskites; Dielectric properties; Optoelectronic applications; Electrochemical impedance spectroscopy; Ionic conductivity

IR-images of PV-modules with potential induced degradation (PID) correlated to monitored string power output - Buerhop, Claudia; Pickel, Tobias; Blumberg, Tiberius; Adams, Jens; Wrana, Simon; Dalsass, Manuel; Zetzmann, Cornelia; Camus, Christian; Hauch, Jens; Brabec, Christoph (Reliability of Photovoltaic Cells, Modules, Components, and Systems IX, 2016)
Many PV-plants suffer from potential induced degradation (PID) which causes severe power reduction of installed PVmodules. Fast and reliable methods to detect PID and evaluate the impact on the module performance are gaining importance. Drone-Assisted IR-inspection is a suitable method. PID affected modules are detected by their characteristic IR-fingerprint, modules with differing number of slightly heated cells occur more frequently at the negative string end. These modules show a degraded IV-curve, lowered Voc and Isc, and electroluminescence (EL)-images with suspicious, dark cells. Also, the measured string power is reduced. For a first quantitative data evaluation the suspicious cell are counted in the IR-images and correlated with the module power. A linear decrease of the module power with increasing number of suspicious cells results. A correlation function for estimating the module power was deduced, which has a mean deviation of less than 7%. This correlation function allows an acceptable approximation of the string power.
Keywords: Degradation; Electroluminescence; IR-imaging; IR-inspection; PID; Potential Induced Degradation; PV-modules; PV-plants; Reliability

IR-imaging and non-destructive loss analysis on thin film solar modules and cells - Adams, Jens; Fecher, Frank W.; Hoga, Felix; Vetter, Andreas; Buerhop, Claudia; Brabec, Christoph (Proceedings of SPIE - The International Society for Optical Engineering, 2014)
CIGS thin film solar modules, despite their high efficiency, may contain three different kinds of macroscopic defects referred to as bulk defects, interface defects and interconnect defects. These occur due to the film's sensitivity to inhomogeneities during the manufacturing process and decreasing the electrical power output from a cell or module. In this study, we present infrared (IR) imaging and contactless loss analyses of defects contained in commercially manufactured thin film solar modules. We investigated different relations between the emitted IR-signal (using illuminated lock-in thermography ILIT) and the respective open circuit cell voltage (Voc) as well as the maximum power point (Pmpp). A simulation study, using the 2D finite element method (FEM), provides a deeper understanding as to the impact on electrical performance when defects are present on the cell or module.
Keywords: 2D finite element method; CIGS thin film technology; Contactless; Defects; ILIT; Lock in thermography; Open circuit voltage

IR sensitization of an indene-C60 bisadduct (ICBA) in ternary organic solar cells - Ameri, Tayebeh; Heumüller, Thomas; Min, Jie; Li, Ning; Matt, Gebhard; Scherf, Ullrich; Brabec, Christoph (Energy and Environmental Science, 2013)
This article presents a smart strategy to successfully tackle two main limitations of organic solar cells (OSCs) in one step: the narrow absorption window of polymers as well as the V limitation related to the mono-PCBM. We demonstrate the high OSC performance of >5% in the combination of a fullerene multiadduct, i.e. indene-C60 bisadduct (ICBA) with a low bandgap polymer employing the concept of ternary OSCs. Solar cells achieving a fill factor (FF) of >60% along with high quantum efficiency in the near IR region are demonstrated for ternary composites consisting of P3HT, the fullerene-bisindene adduct of ICBA and a low bandgap copolymer sensitizer. Using P3HT as an efficient transport matrix with non-Langevin recombination dynamics allowed us to limit and overcome the otherwise dominant recombination losses of the indene-C60 bisadduct-low bandgap copolymer blends. The success of this strategy resulted in a relative efficiency improvement of over 25%. © 2013 The Royal Society of Chemistry.

ITO-Free and Fully Solution-Processed Semitransparent Organic Solar Cells with High Fill Factors - Guo, Fei; Zhu, Xiangdong; Forberich, Karen; Krantz, Johannes; Stubhan, Tobias; Salinas Batallas, Michael; Halik, Marcus; Spallek, Stefanie; Butz, Benjamin; Spiecker, Erdmann; Ameri, Tayebeh; Li, Ning; et al. (Advanced Energy Materials, 2013)
Organic photovoltaic (OPV) solar cells that can be simply processed from solution are in the focus of the academic and industrial community because of their enormous potential to reduce cost. One big challenge in developing a fully solution-processed OPV technology is the design of a well-performing electrode system, allowing the replacement of ITO. Several solution-processed electrode systems were already discussed, but none of them could match the performance of ITO. Here, we report efficient ITO-free and fully solution-processed semitransparent inverted organic solar cells based on silver nanowire (AgNW) electrodes. To demonstrate the potential of these AgNW electrodes, they were employed as both the bottom and top electrodes. Record devices achieved fill factors as high as 63.0%, which is comparable to ITO based reference devices. These results provide important progress for fully printed organic solar cells and indicate that ITO-free, transparent as well as non-transparent organic solar cells can indeed be fully solution-processed without losses. Indium tin oxide (ITO)-free and fully solution-processed organic solar cells are demonstrated by employing AgNW as both the bottom and top electrodes, in conjunction with Al-ZnO and poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) as charge extraction layers. Devices with electrical fill factor (FF) up to 63.0% and fully retained open circuit voltage (V) are achieved, indicating that superior optoelectronic and film quality properties of the two interlayers are perfectly compatible to AgNW electrodes. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Joint Super-Resolution and Rectification for Solar Cell Inspection - Hoffmann, Mathis; Köhler, Thomas; Doll, Bernd; Schebesch, Frank; Talkenberg, Florian; Peters, Ian Marius; Brabec, Christoph; Maier, Andreas; Christlein, Vincent (IEEE Journal of Photovoltaics, 2021)
Visual inspection of solar modules is an important monitoring facility in photovoltaic power plants. Since a single measurement of fast CMOS sensors is limited in spatial resolution and often not sufficient to reliably detect small defects, we apply multi-frame super-resolution (MFSR) to a sequence of low resolution measurements. In addition, the rectification and removal of lens distortion simplifies subsequent analysis. Therefore, we propose to fuse this pre-processing with standard MFSR algorithms. This is advantageous, because we omit a separate processing step, the motion estimation becomes more stable and the spacing of high-resolution (HR) pixels on the rectified module image becomes uniform w.r.t. the module plane, regardless of perspective distortion. We present a comprehensive user study showing that MFSR is beneficial for defect recognition by human experts and that the proposed method performs better than the state of the art. Furthermore, we apply automated crack segmentation and show that the proposed method performs 3x better than bicubic upsampling and 2x better than the state of the art for automated inspection.

Key parameters of efficient phosphor-filled luminescent down-shifting layers for photovoltaics - Solodovnyk, Anastasiia; Lipovsek, Benjamin; Riedel, Daniel; Forberich, Karen; Stern, Edda; Batentschuk, Miroslaw; Krc, Janez; Topic, Marko; Brabec, Christoph (Journal of Optics A-Pure and Applied Optics, 2017)
Spectral management is one of the promising ways to increase the efficiency of modern photovoltaic devices. We study the performance of phosphor-filled luminescent down-shifting (LDS) layers. We focus on four powder phosphors with refractive indices in the range of 1.66-1.84 and similar particle size distributions. Using experimental characterization as well as 3D optical simulations, we identify key parameters of the phosphor particles and LDS layers that primarily affect the optical transmittance, absorptance, and photoluminescence quantum yield of the layers. We investigate the influence of the medium located beneath the LDS layer and reveal a strong increase in the performance when the layer is applied directly onto the solar cell. Finally, the optimal combination of the particle, binder and layer parameters that render the highest performance of the LDS layers are also indicated and discussed. © 2017 IOP Publishing Ltd.
Keywords: absorptance; phosphors; photoluminescence quantum yield; photovoltaics; transmittance

Key Parameters Requirements for Non-Fullerene-Based Organic Solar Cells with Power Conversion Efficiency > 20% - Firdaus, Yuliar; Le Corre, Vincent Marc; Khan, Jafar I.; Kan, Zhipeng; Laquai, Frederic; Beaujuge, Pierre M; Anthopoulos, Thomas D (Advanced Science, 2019)
The reported power conversion efficiencies (PCEs) of nonfullerene acceptor (NFA) based organic photovoltaics (OPVs) now exceed 14% and 17% for single-junction and two-terminal tandem cells, respectively. However, increasing the PCE further requires an improved understanding of the factors limiting the device efficiency. Here, the efficiency limits of single-junction and two-terminal tandem NFA-based OPV cells are examined with the aid of a numerical device simulator that takes into account the optical properties of the active material(s), charge recombination effects, and the hole and electron mobilities in the active layer of the device. The simulations reveal that single-junction NFA OPVs can potentially reach PCE values in excess of 18% with mobility values readily achievable in existing material systems. Furthermore, it is found that balanced electron and hole mobilities of >10(-3) cm(2) V-1 s(-1) in combination with low nongeminate recombination rate constants of 10(-12) cm(3) s(-1) could lead to PCE values in excess of 20% and 25% for single-junction and two-terminal tandem OPV cells, respectively. This analysis provides the first tangible description of the practical performance targets and useful design rules for single-junction and tandem OPVs based on NFA materials, emphasizing the need for developing new material systems that combine these desired characteristics.
Keywords: bulk-heterojunction solar cells; drift-diffusion model; nonfullerene acceptors; numerical device simulations; organic photovoltaics; tandem devices

Kooperative Promotionen mit Fachhochschulen in Zusammenarbeit mit der technischen Fakultät der Universität Erlangen-Nürnberg; erschienen in „Ingenieurpromotion – Stärken und Qualitätssicherung, Beiträge eines gemeinsamen Symposiums von acatech, TU9, ARGE TU/TH und 4ing - Wellmann, Peter (Ingenieurpromotion – Stärken und Qualitätssicherung, 2011)

Large Area Growth of Cubic Silicon Carbide Using Close Space PVT by Application of Homoepitaxial Seeding - Kollmuß, Manuel; Schöler, Michael; Anzalone, R.; Mauceri, M.; La Via, F.; Wellmann, Peter (Materials Science Forum, 2022)
One setback that hinders the breakthrough of cubic silicon carbide is the lack of suitable seeding material for sublimation growth methods such as PVT. We present the growth of large area cubic silicon carbide material, up to a diameter of 100 mm, with a sublimation growth process called close spaced PVT (CS-PVT). Freestanding 3C-SiC seeding layers were grown by a homoepitaxial CVD process. Subsequently CS-PVT was used to grow crystals up to a thickness of 1 mm. To prevent backside sublimation a carbon containing layer was applied as protection. Due to the presence of a wafer bow as well as a rough backside of the used seeds additional effort was necessary to apply the coating. After growth no visible curvature was present independent of the grown layer thickness and sample size. Raman spectroscopy was performed on the seeds and grown crystals, showing that the overall stress level of the material was reduced by CS-PVT.
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Keywords: 3C-SiC; bow reduction; large-area growth; stress reduction; Sublimation growth

Large-area organic photovoltaic modules with 14.5% certified world record efficiency - Basu, Robin; Gumpert, Fabian; Lohbreier, Jan; Morin, Pierre Olivier; Vohra, Varun; Liu, Yang; Zhou, Yinhua; Brabec, Christoph; Egelhaaf, Hans-Joachim; Distler, Andreas (Joule, 2024)
Organic photovoltaics (OPVs) have experienced a significant increase in power conversion efficiency (PCE) recently, now approaching 20% on small-cell level. Since the efficiencies on the module level are still substantially lower, focused upscaling research is necessary to reduce the gap between cells and modules. In this work, we present the upscaling of PM6:Y6-C12:PC61BM-based devices, processed in ambient air from non-halogenated solvents, from small-area cells to large-area modules with barely any performance loss. Supported by computational fluid dynamics simulations, an accelerated blade coating process that enables homogeneous coatings with <5% thickness deviation over 200 cm² is developed. Additional finite element method simulations are used to optimize the module layout and minimize the inevitable losses caused by electrode resistances and inactive interconnect areas to 1.9% and 3.5%, respectively. Finally, a 204-cm² OPV module with a certified PCE of 14.5% (15.0% on active area) is fabricated, which constitutes the new world record.
CRIS-Team Scopus Importer:2024-04-05
Keywords: certified world record efficiency; FEM simulations; laser patterning; OPVs; organic photovoltaics; process optimization; solar modules; solution-processed in ambient air

Large area slot-die coated organic solar cells on flexible substrates with non-halogenated solution formulations - Machui, Florian; Lucera, Luca; Spyropoulos, Georgios; Cordero, Johann; Ali, Abid Shaukat; Kubis, Peter; Ameri, Tayebeh; Voigt, Monika; Brabec, Christoph (Solar Energy Materials and Solar Cells, 2014)
The transfer from lab scale to industrial application is one of the challenges for organic photovoltaics. For this, non halogenated formulations are a decisive need for the upscaling process, as are roll-to-toll (R2R) compatible methods. Devices processed with o-xylene using slot-die coating as a sheet-to-sheet technique show a reduced efficiency on a larger scale compared to lab scale solar cells. By using a mixture of high and low volatile solvents which selectively dissolve one component, the film homogeneity and the efficiency is dramatically improved. The slot-die coated active layers for solar cells processed from non-halogenated solvents show device efficiencies above 3% on flexible substrates.
Keywords: Film homogeneity; Flexible substrates; Ink formulation; Organic photovoltaics; Slot-die coating; Solvent

Laser Cutting of Metal-Halide-Perovskite Wafers for X-Ray Detector Integration - Deumel, Sarah; Reg, Yvonne; Huerdler, Judith E.; Hussenether, Lukas; Schmidt, Oliver; Barabash, Anastasia; Heiß, Wolfgang; Tedde, Sandro F. (Advanced Materials Interfaces, 2022)
To realize various applications, structuring methods of metal-halide perovskites are of great importance. Most of the common techniques have focused on thin layers and suffer from limitations for thick layers. But thicknesses of several hundred micrometers are necessary, especially for the application field of medical X-ray detection. In order to scale perovskite-based X-ray detectors from small laboratory devices to realistic product sizes, new manufacturing strategies such as laser cutting are necessary. Here the potential of structuring any configurable geometry out of thick, freestanding methylammonium lead iodide (MAPbI3) wafers with ultrashort pulse (USP) laser at a wavelength of 1064 nm, is shown. A small difference in the laser parameters causes a significant variation of the perovskite from material decomposition to almost no effects. With the chosen parameter set of the USP laser, the MAPbI3 wafer can be shaped so that just slight changes in the morphology and no difference in the X-ray performance can be seen. This method offers the possibility of scaling up perovskite X-ray detectors in the future without significant signal loss.
CRIS-Team Scopus Importer:2022-05-06
Keywords: patterning; perovskites; structuring; ultrashort pulse laser; X-ray detection

Laser process for extended silicon thin film solar cells - Hessmann, M. T.; Kunz, T.; Burkert, I.; Gawehns, N.; Schaefer, L.; Frick, T.; Schmidt, Michael; Meidel, B.; Auer, R.; Brabec, Christoph (Thin Solid Films, 2011)
We present a large area thin film base substrate for the epitaxy of crystalline silicon. The concept of epitaxial growth of silicon on large area thin film substrates overcomes the area restrictions of an ingot based monocrystalline silicon process. Further it opens the possibility for a roll to roll process for crystalline silicon production. This concept suggests a technical pathway to overcome the limitations of silicon ingot production in terms of costs, throughput and completely prevents any sawing losses. The core idea behind these thin film substrates is a laser welding process of individual, thin silicon wafers. In this manuscript we investigate the properties of laser welded monocrystalline silicon foils (100) by micro-Raman mapping and spectroscopy. It is shown that the laser beam changes the crystalline structure of float zone grown silicon along the welding seam. This is illustrated by Raman mapping which visualizes compressive stress as well as tensile stress in a range of - 147.5 to 32.5 MPa along the welding area. © 2011 Elsevier B.
Keywords: Crystalline silicon; Laser beam welding; Raman spectroscopy; Thin films

Laser structuring of crystalline silicon thin-film solar cells on opaque foreign substrates - Kunz, T.; Gazuz, V.; Hessmann, M. T.; Gawehns, N.; Burkert, I.; Brabec, Christoph (Solar Energy Materials and Solar Cells, 2011)
Crystalline silicon thin-film solar cells were fabricated on graphite substrates. A laser ablation process was developed for edge isolation of the thin-film cells. The shunt resistance was comparable to otherwise identical cells isolated by plasma etching, while the reproducibility of the laser isolation process was higher. The solar cells were characterized by currentvoltage and light beam induced current measurements (LBiC). No interference was detected along the ablated edges. Spatial variations of the minority carrier lifetime are attributed to the grain structure of the seeding layer obtained by the zone melting recrystallization (ZMR). © 2011 Elsevier B.V.
Keywords: Crystalline thin-film silicon; Edge isolation; Graphite substrate; Laser processing

Laser Writing of Scalable Single Color Centers in Silicon Carbide - Chen, Yu-Chen; Salter, Patrick S.; Niethammer, Matthias; Widmann, Matthias; Kaiser, Florian; Nagy, Roland; Morioka, Naoya; Babin, Charles; Erlekampf, Jürgen; Berwian, Patrick; Booth, Martin J.; Wrachtrup, Joerg (Nano Letters, 2019)
Single photon emitters in silicon carbide (SiC) are attracting attention as quantum photonic systems (Awschalom et al. Nat. Photonics 2018, 12, 516-527; Atatüre et al. Nat. Rev. Mater. 2018, 3, 38-51). However, to achieve scalable devices, it is essential to generate single photon emitters at desired locations on demand. Here we report the controlled creation of single silicon vacancy (V Si ) centers in 4H-SiC using laser writing without any postannealing process. Due to the aberration correction in the writing apparatus and the nonannealing process, we generate single V Si centers with yields up to 30%, located within about 80 nm of the desired position in the transverse plane. We also investigated the photophysics of the laser writing V Si centers and concluded that there are about 16 photons involved in the laser writing V Si center process. Our results represent a powerful tool in the fabrication of single V Si centers in SiC for quantum technologies and provide further insights into laser writing defects in dielectric materials.
CRIS-Team Scopus Importer:2020-10-30
Keywords: arrays; laser writing; scalable; silicon carbide; Silicon vacancy defect

Last Generation Solar Cells in Outer Space: A STEM Outreach Project with Middle and High School Students in Colombia - Perea, Jose Dario; Gasca, Diana Carolina; Echeverry-Prieto, Ghisliane; Quiroga-Fonseca, Valentina; Orozco-Donneys, Carolina; Díaz-Montealegre, Leidy Catherine; Ortiz, Alejandro; Molina, Giovanny; Cruz, Daniel; Persad, Aaron; Redd-Kantareddy, Sai Nithin; Wachsmuth, Josua; et al. (European Journal of STEM Education, 2021)
As part of an unprecedented collaborative outreach effort, we implemented an innovative STEM outreach project, where more than 80 middle and high school students from different traditionally underrepresented school districts in Colombia-with no previous knowledge on material science or photovoltaics-created Last Generation Solar Cells (LGSCs) that were part of several suborbital spaceflight missions. As a result, the students were able to contrast visual and instrumental data obtained from the solar cells and modules that were launched to space with similar samples that remained on earth to measure the degradation that occurs during spaceflight conditions. At the same time, the students that participated were able to cultivate their curiosity, strengthen their scientific skills and increase their interest in pursuing careers in STEM fields. These experiences were possible thanks to an extraordinary collaborative network between public and private entities and the use of project-based education as a powerful driver of development, especially for low-to-middle-income countries, such as Colombia. Here, we share our methodology for constructing photovoltaic devices in rural settings, and we show the progression and impact of this novel scientific outreach project.
CRIS-Team Scopus Importer:2023-03-07
Keywords: last generation solar cells; organic solar cells; science outreach; STEM education

Lateral boron distribution in polycrystalline SiC source materials - Linnarsson, Margareta K.; Kaiser, Michl; Liljedahl, Rickard; Jokubavicius, Valdas; Ou, Yiyu; Wellmann, Peter; Ou, Haiyan; Syväjärvi, Mikael (Materials Science Forum, 2013)
Polycrystalline SiC containing boron and nitrogen are used in growth of fluorescent SiC for white LEDs. Two types of doped polycrystalline SiC have been studied in detail with secondary ion mass spectrometry: sintered SiC and poly-SiC prepared by sublimation in a physical vapor transport setup. The materials are co-doped materials with nitrogen and boron to a concentration of 1x10(18) cm(-3) and 1x10(19) cm(-3), respectively. Depth profiles as well as ion images have been recorded. According to ocular inspection, the analyzed poly-SiC consists mainly of 4H-SiC and 6H-SiC grains. In these grains, the boron concentration is higher and the nitrogen concentration is lower in the 6H-SiC compared to the 4H-SiC polytype. No inter-diffusion between grains is observe
Keywords: Boron; Dopant Distribution; SIMS

Layer-by-layer processed binary all-polymer solar cells with efficiency over 16% enabled by finely optimized morphology - Zhang, Yue; Wu, Baoqi; He, Yakun; Deng, Wanyuan; Li, Jingwen; Li, Junyu; Qiao, Nan; Xing, Yifan; Yuan, Xiyue; Li, Ning; Brabec, Christoph; Wu, Hongbin; et al. (Nano Energy, 2022)
Optimal active layer morphology is a prerequisite for high-efficiency all-polymer solar cells (all-PSCs). Herein, we report that the vertical phase separation as well as microstructures of the polymer donor and acceptor can be finely optimized in layer-by-layer (LbL) processed all-PSCs. By using 1-chloronaphthalene as the solvent additive during the deposition of the polymer acceptor in the top layer and applying thermal annealing on the entire active layer, bulk-heterojunction like morphology with favorable vertical composition distribution, improved lamellar ordering of the polymer donor (PBDB-T), and the formation of polymer fibrils of the polymer acceptor (PYT) have been realized simultaneously. This favorable morphology led to greatly enhanced exciton splitting efficiency, reduced trap density, improved charge transport, and suppressed charge recombination loss. As a result, the LbL processed all-PSCs of PBDB-T/PYT afforded a power conversion efficiency (PCE) of 16.05%, which is one of the highest PCEs for binary all-PSCs. Moreover, a fill factor (FF) of 0.77 has been obtained, which is the highest value for all-PSCs based on polymerized small molecule acceptors up to date. This work demonstrates an effective strategy for morphology optimization of LbL processed all-PSCs, which will greatly contribute to efficiency breakthrough.
CRIS-Team Scopus Importer:2022-01-07
Keywords: Active layer morphology; All-polymer solar cells; High-efficiency; Layer-by-layer processing; Vertical composition distribution

Lead-Free Perovskite Cs2AgxNa1-xBiyIn1-yCl6 Microcrystals for Scattering-Fluorescent Luminescent Solar Concentrators - Kong, Mengqin; Osvet, Andres; Forberich, Karen; Barabash, Anastasia; Erban, Christof; Batentschuk, Miroslaw; Brabec, Christoph (ACS Applied Materials and Interfaces, 2025)
In recent years, luminescent solar concentrators (LSCs) have gained a renaissance as a pivotal transparent photovoltaic (PV) for building-integrated photovoltaics (BIPVs). However, most of the studies focused on light-selective LSCs, and less attention was paid to the utilization of the full solar spectrum. In this study, a lead-free microcrystal Cs2AgxNa1-xBiyIn1-yCl6 (CANBIC) perovskite phosphor is demonstrated to have bifunctional effects of luminescent down-shifting (LDS) and light scattering for the fabrication of LSCs, realizing light response from ultraviolet (UV) to NIR regions by an edge-mounted Si solar cell. The optimized CANBIC content (30 mg) in an LSC realizes the best optical efficiency (ηopt) of 5.40% and an average visible transmission (AVT) of >50%. This contributes to the improvement in short circuit current density (JSC) up to 1.232 mA/cm2 for the LSC-PV system (one-edge mounted Si solar cell) as a result of the best power conversion efficiencies (PCEs) of 0.463% and 1.852% for the LSC-PV and LSC-4PV systems (four-edge mounted Si solar cells), respectively. An Al foil is applied as a reflection background in the LSC-4PV system, and a champion PCE of 3.14% is realized due to an improved JSC of up to 7.94 mA/cm2 in total. Furthermore, the LSC maintains superior stability under exposure to continuous ultraviolet illumination or in ambient air.
CRIS-Team Scopus Importer:2025-01-31
Keywords: Cs; lead-free perovskite; light scattering; luminescent down-shifting; luminescent solar concentrator; photovoltaic

Lifetime and Degradation of Pre-damaged PV-Modules - Field study and lab testing - Buerhop, Claudia; Wirsching, Sven; Gehre, Simon; Pickel, Tobias; Winkler, Thilo; Bemm, Andreas; Mergheim, Julia; Camus, Christian; Brabec, Christoph; Hauch, Jens (Conference record of the IEEE Photovoltaic Specialists Conference, 2017)
The presence of pre-cracked PV-modules in modern PV-plants is well-known. The evolution and actual impact of the cracks on electrical yield under real operation conditions is not yet understood but of great relevance. Established standards cannot reveal the relevant effects. Therefore, a unique threefold analysis is applied: 1) field exposure, 2) using a new accelerated loading test, and 3) Finite Elements (FEM) simulations. For the first time, we present comparative Electroluminescence (EL-) images recorded in the field and during load testing. Crack growth is studied in terms of the monitored weather conditions and the applied load simulating static snow and wind loads.

Lifetime and Degradation of Pre-damaged PV-Modules – Field study and lab testing - Buerhop, Claudia; Wirsching, Sven; Gehre, Simon; Pickel, Tobias; Winkler, Thilo; Bemm, Andreas; Mergheim, Julia; Camus, Christian; Hauch, Jens; Brabec, Christoph (44th IEEE Photovoltaic Specialists Conference, 2017)
The presence of pre-cracked PV-modules in modern PV-plants is well-known. The evolution and actual impact of the cracks on electrical yield under real operation conditions is not yet understood but of great relevance. Established standards cannot reveal the relevant effects. Therefore, a unique threefold analysis is applied: 1) field exposure, 2) using a new accelerated loading test, and 3) Finite Elements (FEM) simulations. For the first time, we present comparative Electroluminescence (EL-) images recorded in the field and during load testing. Crack growth is studied in terms of the monitored weather conditions and the applied load simulating static snow and wind loads.

Ligand-assisted thickness tailoring of highly luminescent colloidal CH3NH3PbX3 (X = Br and I) perovskite nanoplatelets - Levchuk, Ievgen; Herre, Patrick; Brandl, Marco; Osvet, Andres; Hock, Rainer; Peukert, Wolfgang; Schweizer, Peter; Spiecker, Erdmann; Batentschuk, Miroslaw; Brabec, Christoph (Chemical Communications, 2017)
Quantum size-confined CHNHPbX (X = Br and I) perovskite nanoplatelets with remarkably high photoluminescence quantum yield (up to 90%) were synthesized by ligand-assisted re-precipitation. Thickness-tunability was realized by varying the oleylamine and oleic acid ligand ratio. This method allows tailoring the nanoplatelet thickness by adjusting the number of unit cell monolayers. Broadly tunable emission wavelengths (450-730 nm) are achieved via the pronounced quantum size effect without anion-halide mixing.

Ligand Tuning of Localized Surface Plasmon Resonances in Antimony-Doped Tin Oxide Nanocrystals - Balitskii, Olexiy; Mashkov, Oleksandr; Barabash, Anastasia; Rehm, Viktor; Afify, Hany A.; Li, Ning; Hammer, Maria; Brabec, Christoph; Eigen, Andreas; Halik, Marcus; Yarema, Olesya; Yarema, Maksym; et al. (Nanomaterials, 2022)
Aliovalent-doped metal oxide nanocrystals exhibiting localized surface plasmons (LSPRs) are applied in systems that require reflection/scattering/absorption in infrared and optical transparency in visible. Indium tin oxide (ITO) is currently leading the field, but indium resources are known to be very restricted. Antimony-doped tin oxide (ATO) is a cheap candidate to substitute the ITO, but it exhibits less advantageous electronic properties and limited control of the LSPRs. To date, LSPR tuning in ATO NCs has been achieved electrochemically and by aliovalent doping, with a significant decrease in doping efficiency with an increasing doping level. Here, we synthesize plasmonic ATO nanocrystals (NCs) via a solvothermal route and demonstrate ligand exchange to tune the LSPR energies. Attachment of ligands acting as Lewis acids and bases results in LSPR peak shifts with a doping efficiency overcoming those by aliovalent doping. Thus, this strategy is of potential interest for plasmon implementations, which are of potential interest for infrared upconversion, smart glazing, heat absorbers, or thermal barriers.
CRIS-Team WoS Importer:2022-10-28

Light capacitances in silicon and perovskite solar cells - Almora, Osbel; Garcia-Belmonte, Germà (Solar Energy, 2019)
The framework on which the physics of silicon solar cells (SiSCs) is based robustly predicts dependences of capacitance on light intensity and voltage, even when most recent innovations are considered as the incorporation of transition metal oxide/Si heterojunctions. However, perovskite solar cells (PSCs) challenge most of the established paradigms, claiming for rethinking of known theories and devising novel models. Here we tackle this scenario by probing and comparing light-induced capacitance responses yielded by these two major exponents in the field of photovoltaic research. SiSCs light capacitances can be easily interpreted in the framework of the so-called chemical capacitance. Latest approaches addressing the intriguing low-frequency capacitive features of PSCs are outlined and compared. Here, apparent similarities and differences between both photovoltaic technologies are highlighted, concerning the observation of light capacitances of chemical origin. It is concluded that, contrary to that occurring in SiSCs, bulk electronic chemical capacitances are not straightforwardly observed in PSCs. As capacitive features exhibited by PSCs are believed to be critically connected to performance degradation and device instability, future research and explanation directions are proposed here for advancing in the understanding of this challenging photovoltaic technology.
CRIS-Team Scopus Importer:2019-08-02
Keywords: Capacitance; Dielectric relaxation; Light; Perovskites; Silicon; Solar cells

Light extraction from OLEDs for lighting applications through light scattering - Bathelt, Robert; Buchhauser, D.; Gärditz, C.; Paetzold, Ralph; Wellmann, Peter (Organic Electronics, 2007)
Theoretical considerations expect an increase of outcoupling efficiency of up to 70%. Experimental results yield an increase of outcoupling efficiency of about 22%. A software model based on raytracing to simulate light outcoupling from OLEDs through a scattering layer is introduced to gain a deeper understanding of the light extraction mechanism. We found that the scattering anisotropy factor g determined using the Henyey-Greenstein phase function and the effective absorbance of the OLED device have strong impact on outcoupling efficiency. (c) 2006 Elsevier B.V. All rights reserved.
Keywords: OLED; Lighting; Outcoupling enhancement; Light scattering; Simulation; Raytracing

Light harvesting enhancement upon incorporating alloy structured CdSeXTe1−X quantum dots in DPP:PC61BM bulk heterojunction solar cells - Soltani, Rezvan; Katbab, Ali Asghar; Schaumberger, Kerstin; Gasparini, Nicola; Brabec, Christoph; Rechberger, Stefanie; Spiecker, Erdmann; Alabau, Antoni Gimeno; Ruland, Andres; Saha, Avishek; Guldi, Dirk Michael; Sgobba, Vito; et al. (Journal of Materials Chemistry C, 2017)
Hybrid solar cells based on the pDPP5T-2 electron donating polymer, [6,6]-phenyl-C-butyric acid methyl ester (PCBM) and cadmium selenide telluride (CdSeTe) quantum dots (QDs) are fabricated and their photovoltaic performance and optoelectronic properties are investigated as a function of QD loading. The power conversion efficiency (PCE) of hybrid solar cells is improved up to 5.11% for the device containing 4 wt% of QDs which is mainly due to the enhancement in short circuit current density (J) resulting from increased light harvesting. A full-fledged study is performed on the microstructure, charge transfer/transport and recombination mechanisms of our ternary hybrid solar cells by employing various advanced techniques. The transmission electron microscopy (TEM) results reveal the non-agglomerated and uniform distribution of the CdSeTe QDs within the pDPP5T-2:PCBM host matrix at low QD concentrations. Transient absorption spectroscopy (TAS) showed a slower charge carrier recombination rate due to the introduction of QDs into the photoactive layer. It can be attributed to the more efficient exciton dissociation in ternary systems. These findings are consistent with the photovoltaic properties of the device.
Keywords: Engineering controlled terms: Absorption spectroscopy; Butyric acid; Cadmium compounds; Cadmium telluride; Charge transfer; Heterojunctions; High resolution transmission electron microscopy; Nanocrystals; Polymer solar cells; Semiconductor quantum dots; Solar power generation; Transmission electron microscopy Bulk heterojunction solar cells; Charge carrier recombination; Light harvesting enhancement; Optoelectronic properties; Photovoltaic performance; Power conversion efficiencies; Recombination mechanisms; Transient absorption spectroscopies Engineering main heading: Solar cells

Light intensity modulated impedance spectroscopy (LIMIS) in all-solid-state solar cells at open-circuit - Almora, Osbel; Zhao, Yicheng; Du, Xiaoyan; Heumüller, Thomas; Matt, Gebhard; Garcia-Belmonte, Germà; Brabec, Christoph (Nano Energy, 2020)
Potentiostatic impedance spectroscopy (IS) is a well-established characterization technique for elucidating the electric resistivity and capacitive features of materials and devices. For solar cells, by applying a small voltage perturbation the current signal is recorded and the recombination processes and defect distributions can be accessed. In this work, a photo-impedance approach, named “light intensity modulated impedance spectroscopy” (LIMIS), is first time tested in all-solid-state photovoltaics by individually recording photocurrent (IMPS) and photovoltage (IMVS) responsivity signals due to a small light perturbation at open-circuit (OC), and combining them: LIMIS = IMVS/IMPS. The experimental LIMIS spectra from silicon, organic, and perovskite solar cells are presented and compared with IS. Our theoretical analyses, including equivalent circuit models, show a correction to the lifetimes values by obtaining the total differential resistances and capacitances combining IS and LIMIS. This correction addresses some discrepancies among different techniques, as also shown with photo-induced transient photovoltage. The experimental differences between IS and LIMIS proves the unsuitability of the superposition principle and suggest a bias-dependent photo-current correction to the empirical Shockley equation of the steady-state current at different illumination intensities around OC. In addition, new features are reported for the low-frequency capacitance of perovskite solar cells.
CRIS-Team Scopus Importer:2020-07-31
Keywords: Charge carrier generation rate; Impedance spectroscopy; Light intensity modulation; Perovskites; Photocurrent; Solar cells

Light management and light manipulation technologies for thin film photovoltaics applications - Brabec, Christoph; Batentschuk, Miroslaw; Forberich, Karen (European Quantum Electronics Conference, EQEC 2015, 2015)

Light propagation in phosphor-filled matrices for photovoltaic PL down-shifting - Solodovnyk, Anastasiia; Lipovsek, Benjamin; Forberich, Karen; Stern, Edda; Batentschuk, Miroslaw; Topic, Marko; Brabec, Christoph (Reflection, Scattering, and Diffraction from Surfaces IV, 2014)
Efficient transparent light converters have received lately a growing interest from optical device industries (LEDs, PV, etc.). While organic luminescent dyes were tested in PV light-converting application, such restrictions as small Stokes shifts, short lifetimes, and relatively high costs must yet be overcome. Alternatively, use of phosphors in transparent matrix materials would mean a major breakthrough for this technology, as phosphors exhibit long-term stability and are widely available. For the fabrication of phosphor-filled layers tailored specifically for the desired application, it is of great importance to gain deep understanding of light propagation through the layers, including the detailed optical interplay between the phosphor particles and the matrix material. Our measurements show that absorption and luminescent behavior of the phosphors and especially the scattering of light by the phosphor particles play an important role. In this contribution we have investigated refractive index difference between transparent binder and phosphors. Commercially available highly luminescent UV and near-UV absorbing μm-sized powder is chosen for the fabrication of phosphor-filled layers with varied refractive index of transparent polymer matrix, and well-defined particle size distributions. Solution-processed thick layers on glass substrates are optically analyzed and compared with simulation results acquired from CROWM, a combined wave optics/ray optics home-built software. The results demonstrate the inter-dependence of the layer parameters, prove the importance of careful optimization steps required for fabrication of efficient light converting layers, and, thus, show a path into the future of this promising approach.
Keywords: Light absorption; Matrix; Mie scattering; Phosphor particles; Ray-tracing; Refractive index; Solution processed layers

Limitations during Vapor Phase Growth of Bulk (100) 3C-SiC Using 3C-SiC-on-SiC Seeding Stacks - Schuh, Philipp; Steiner, Johannes; La Via, Francesco; Mauceri, Marco; Zielinski, Marcin; Wellmann, Peter (Materials, 2019)
The growth of 3C-SiC shows technological challenges, such as high supersaturation, a silicon-rich gas phase and a high vertical temperature gradient. We have developed a transfer method creating high-quality 3C-SiC-on-SiC (100) seeding stacks, suitable for use in sublimation “sandwich” epitaxy (SE). This work presents simulation data on the change of supersaturation and the temperature gradient between source and seed for the bulk growth. A series of growth runs on increased source to seed distances was characterized by XRD and Raman spectroscopy. Results show a decrease in quality in terms of single-crystallinity with a decrease in supersaturation. Morphology analysis of as-grown material indicates an increasing protrusion dimension with increasing thickness. This eect limits the achievable maximal thickness. Additional polytype inclusions were observed, which began to occur with low supersaturation (S 0.06) and prolonged growth (increase of carbon gas-species).<br
Keywords: 3C-SiC; physical vapor transport (PVT); sublimation sandwich; supersaturation; bulk

Lithium-Directed Transformation of Amorphous Iridium (Oxy)hydroxides To Produce Active Water Oxidation Catalysts - Esquius, Jonathan Ruiz; Morgan, David J.; Siller, Gerardo Algara; Gianolio, Diego; Aramini, Matteo; Lahn, Leopold; Kasian, Olga; Kondrat, Simon A.; Schloegl, Robert; Hutchings, Graham J.; Arrigo, Rosa; Freakley, Simon J. (Journal of the American Chemical Society, 2022)
The oxygen evolution reaction (OER) is crucial to future energy systems based on water electrolysis. Iridium oxides are promising catalysts due to their resistance to corrosion under acidic and oxidizing conditions. Highly active iridium (oxy)hydroxides prepared using alkali metal bases transform into low activity rutile IrO2 at elevated temperatures (>350 °C) during catalyst/electrode preparation. Depending on the residual amount of alkali metals, we now show that this transformation can result in either rutile IrO2 or nano-crystalline Li-intercalated IrOx. While the transition to rutile results in poor activity, the Li-intercalated IrOx has comparative activity and improved stability when compared to the highly active amorphous material despite being treated at 500 °C. This highly active nanocrystalline form of lithium iridate could be more resistant to industrial procedures to produce PEM membranes and provide a route to stabilize the high populations of redox active sites of amorphous iridium (oxy)hydroxides.
CRIS-Team Scopus Importer:2023-03-29

Local Observation of Phase Segregation in Mixed-Halide Perovskite. - Tang, Xiaofeng; van den Berg, Marius; Gu, Ening; Horneber, Anke; Matt, Gebhard; Osvet, Andres; Meixner, Alfred J.; Zhang, Dai; Brabec, Christoph (Nano Letters, 2018)
Mixed-halide perovskites have emerged as promising materials for optoelectronics due to their tunable bandgap in the entire visible region. A challenge remains however in the photo-induced phase-segregation, narrowing the bandgap of mixedhalide perovskites under illumination thus restricting applications. Here we use a combination of spatially-resolved and bulk measurements to give an in-depth insight into this important yet unclear phenomenon. We demonstrate that photo-induced phase-segregation in mixed-halide perovskites selectively occurs at the grain boundaries rather than within the grain centers by using shear-force scanning probe microscopy in combination with confocal optical spectroscopy. Such difference is further evidenced by light-biased bulk Fourier-transform photocurrent spectroscopy, which shows the iodine-rich domain as a minority phase coexisting with the homogenously mixed phase during illumination. By mapping the surface potential of mixed-halide perovskites, we evidence the higher concentration of positive space charge near grain boundary possibly provides the initial driving force for phasesegregation, while entropic mixing dominates the reverse process. Our work offers detailed insight into the microscopic processes occurring at the boundary of crystalline perovskite grains and will support the development of better passivation strategies, ultimately allowing to process environmentally more stable perovskite films.
Keywords: Perovskite; Photovoltaic; Photoluminescence; Phase-segregation; Scanning probe microscopy; Optical spectroscopy

Local structure observation of Sm doped RB6 (R: rare earth)by white neutron atomic resolution holography - Uechi, Shoichi; Kanazawa, Yuki; Fukumoto, Youhei; Ohoyama, Kenji; Lederer, Maximilian; Happo, Naohisha; Hayashi, Kouichi; Matsuura, Wataru; Iga, Humitoshi (ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 2018)
CRIS-Team WoS Importer:2019-07-19

Lock-in thermography as a tool for quality control of photovoltaic modules - Vetter, Andreas; Fecher, Frank; Adams, Jens; Schaeffler, Raymund; Theisen, Jean-Patrick; Brabec, Christoph; Buerhop, Claudia (Energy Science and Engineering, 2013)
In this short communication, we present a method which utilizes contactless ILIT (illuminated lock-in thermography) measurement of a photovoltaic (PV) module and image postprocessing in order to calculate the peak power Pmpp of the module and to study the influence of local defects on the module performance. In total, 103 Copper-Indium-Gallium-Diselenide (CIGS) modules were investigated and the results showed a good correlation (mean error less than 6%) between the calculated IR-signal and the measured Pmpp. We performed our study on CIGS modules but the presented approach is not restricted to CIGS modules. The method provides a valuable tool for PV quality control. We present a method which utilizes contactless ILIT (illuminated lock-in thermography) measurement of PV modules and image postprocessing in order to calculate the peak power of the modules. The method provides a valuable tool for PV quality control. © 2013 Society of Chemical Industry and John Wiley & Sons, Ltd.
Keywords: Engineering controlled terms: Image processingInfrared imagingLocks (fasteners)Photovoltaic cellsQuality assuranceQuality controlSelenium compoundsSolar energySolar power generationThermography (temperature measurement) Compendex keywords Copper indium gallium diselenideGood correlationsIlluminated lock-in thermographiesLocal defectsLockin thermographyModule performancePhotovoltaic modulesPhotovoltaics Engineering main heading: Thermography (imaging)

Long Lived OPV – what are the lifetime limitations of organic solar cells - Brabec, Christoph; Heumüller, Thomas (2022)

Long-Living Holes in Grey Anatase TiO2 Enable Noble-Metal-Free and Sacrificial-Agent-Free Water Splitting - Liu, Ning; Mohajernia, Shiva; Nguyen, Nhat Truong; Hejazi, Seyedsina; Plass, Fabian; Kahnt, Axel; Yokosawa, Tadahiro; Osvet, Andres; Spiecker, Erdmann; Guldi, Dirk Michael; Schmuki, Patrik (Chemsuschem, 2020)
Titanium dioxide has been the benchmark semiconductor in photocatalysis for more than 40 years. Full water splitting, that is, decomposing water into H2 and O2 in stoichiometric amounts and with an acceptable activity, still remains a challenge, even when TiO2-based photocatalysts are used in combination with noble-metal co-catalysts. The bottleneck of anatase-type TiO2 remains the water oxidation, that is, the hole transfer reaction from pristine anatase to the aqueous environment. In this work, we report that “grey” (defect engineered) anatase can provide a drastically enhanced lifetime of photogenerated holes, which, in turn, enables an efficient oxidation reaction of water to peroxide via a two-electron pathway. As a result, a Ni@grey anatase TiO2 catalyst can be constructed with an impressive performance in terms of photocatalytic splitting of neutral water into H2 and a stoichiometric amount of H2O2 without the need of any noble metals or sacrificial agents. The finding of long hole lifetimes in grey anatase opens up a wide spectrum of further photocatalytic applications of this material.
CRIS-Team Scopus Importer:2020-08-21
Keywords: long-living holes; noble-metal-free; sacrificial-agent-free; titanium dioxide; water splitting

Long-range exciton diffusion in molecular non-fullerene acceptors - Firdaus, Yuliar; Le Corre, Vincent Marc; Karuthedath, Safakath; Liu, Wenlan; Markina, Anastasia; Huang, Wentao; Chattopadhyay, Shirsopratim; Nahid, Masrur Morshed; Nugraha, Mohamad I; Lin, Yuanbao; Seitkhan, Akmaral; Basu, Aniruddha; et al. (Nature Communications, 2020)
The short exciton diffusion length associated with most classical organic semiconductors used in organic photovoltaics (5-20nm) imposes severe limits on the maximum size of the donor and acceptor domains within the photoactive layer of the cell. Identifying materials that are able to transport excitons over longer distances can help advancing our understanding and lead to solar cells with higher efficiency. Here, we measure the exciton diffusion length in a wide range of nonfullerene acceptor molecules using two different experimental techniques based on photocurrent and ultrafast spectroscopy measurements. The acceptors exhibit balanced ambipolar charge transport and surprisingly long exciton diffusion lengths in the range of 20 to 47nm. With the aid of quantum-chemical calculations, we are able to rationalize the exciton dynamics and draw basic chemical design rules, particularly on the importance of the end-group substituent on the crystal packing of nonfullerene acceptors.

Long-Term Field Screening by Mobile Ions in Thick Metal Halide Perovskites: Understanding Saturation Currents - Almora, Osbel; Miravet, Daniel; Gelmetti, Ilario; Garcia-Belmonte, Germa (Physica Status Solidi-Rapid Research Letters, 2022)
Metal halide perovskite-based semiconductor devices with micrometer-to-millimeter-thick perovskite layers show a current response upon polarization which evolves up to several hours, transiting several regimes. This is the case of X-ray detectors where the use of absorber perovskites produces instabilities in the dark reverse saturation current hindering the signal processing. Even though these phenomena are often attributed to the electronic–ionic conductivity and the interface phenomena in these perovskites, a proper theoretical description is missing. Herein, the numerical simulation study reproduces the main experimental trends and explains the origin of some of the apparently-always-increasing current transients in thick perovskite samples. The mobile ion concentration and mobility are correlated with three main transport regimes and interpretation and parameterization are provided to the current saturation time in terms of the ionic screening of the electric field toward the interfaces. The final steady-state under reverse polarization is found as diffusion-limited electronic current, which results from abrupt mobile ion depletion proportional to the Debye length in the vicinity of a contact. The conclusions suggest the material optimization of the contact interfaces as a pathway to reduce the long current saturation times in these devices.
CRIS-Team Scopus Importer:2022-09-30
Keywords: charge carrier mobility; Debye length; drift-diffusion simulations; ionic conductivity; metal halide perovskites; semiconductor interfaces; X-ray detectors

Long term outdoor performance evaluation of printed semitransparent organic photovoltaic modules for BIPV/BAPV applications - Feroze, Sarmad; Distler, Andreas; Dong, Lirong; Wagner, Michael; Channa, Iftikhar Ahmed; Hoga, Felix; Brabec, Christoph; Egelhaaf, Hans-Joachim (Energy and Environmental Science, 2024)
Recently, organic photovoltaics (OPV) have achieved power conversion efficiencies (PCE) above 20% thus coming closer to market entry. Building-integrated photovoltaics (BIPV) and building-attached photovoltaics (BAPV) are two key areas where the functional advantages of both OPV and BIPV/BAPV complement each other and thus could pave the way for market penetration of OPV. Herein, we report on large-area, all-solution-processed flexible OPV modules manufactured by a fully roll-to-roll (R2R) method with high levels of process repeatability. The OPV modules show an accelerated lifetime (ALT) of more than 1000 h and 2800 h under the ISOS-L2 and ISOS-D3 testing conditions, respectively. Long-term outdoor monitoring of the OPV modules was conducted in a typical central European climate, considering two distinct mounting angles that hold significant relevance for BIPV installations i.e., 45° inclination with respect to the ground (representing the optimal tilt angle of the site) and 90° vertical mounting (as mostly encountered in BIPV façades). The ISOS-O2 protocol was used as the test standard for outdoor monitoring. The results show that the OPV modules can offer higher daily specific energy yields (YFD), i.e., higher ratios of daily energy yield and STC WP capacity of the module, than a reference mono-crystalline (m-Si) module for BIPV installations typical of a rooftop case (i.e., 45°), whereas for façade integrated cases (i.e., 90°), OPV modules offer YFD values identical to that of m-Si modules. Detailed laboratory investigations reveal that the higher YFD values of the OPV modules at 45° mounting stems from their negligible temperature coefficient of −0.008% °C−1, whereas at 90° mounting, the angle-dependent response of the modules plays a crucial role.
CRIS-Team Scopus Importer:2025-02-04

Long-term power degradation analysis of crystalline silicon PV modules using indoor and outdoor measurement techniques - Carigiet, Fabian; Brabec, Christoph; Baumgartner, Franz P. (Renewable and Sustainable Energy Reviews, 2021)
Annual degradation rates of PV modules are important in the yield prediction. For a high-quality PV module, these rates are lower than the measurement uncertainty of a nominal power measurement performed in todays most advanced certified photovoltaic reference laboratory. Therefore, the analysis requires a well thought out methodology that can compare the data relative to each other or relative to an unused module stored in the dark on an annual base. Over the past 10 years, several multi c-Si and HIT modules have been accurately monitored in a string and single module setup by an outdoor performance measurement system. Additionally, all modules have been dismantled and measured using an indoor flasher measurement system once every year. With this unique measurement setup, the annual degradation rates of multi c-Si modules and HIT modules are quantified based on three different analysis methodologies. The multi c-Si modules showed an average annual degradation rate of 0.18% ± 0.06% and 0.29% ± 0.06% measured by the outdoor and indoor system, respectively. The indoor analysis of the HIT modules yielded an average annual degradation of 0.26% ± 0.05%. That corresponds to half of the degradation observed by the outdoor analysis method. Further evaluations of the performance ratio PR confirmed the results gained by the indoor methodology. The comparison of the standard PR with a temperature-corrected PR’STC for both technologies showed that the benefit of the lower temperature coefficient of the HIT technology is eliminated by its worse low light behaviour.
CRIS-Team Scopus Importer:2021-04-09
Keywords: c-Si solar cell; Degradation rate; Outdoor performance monitoring; Outdoor test field; Performance ratio; Solar simulator measurement

Looking beyond the Surface: The Band Gap of Bulk Methylammonium Lead Iodide - Schuster, Oskar; Wientjes, Peter; Shrestha, Shreetu; Levchuk, Ievgen; Sytnyk, Mykhailo; Matt, Gebhard; Osvet, Andres; Batentschuk, Miroslaw; Heiß, Wolfgang; Brabec, Christoph; Fauster, Thomas; Niesner, Daniel (Nano Letters, 2020)
Despite the intense research on photovoltaic lead halide perovskites, reported optical properties as basic as the absorption onset and the optical band gap vary significantly. To unambiguously answer the question whether the discrepancies are a result of differences between bulk and "near-surface" material, we perform two nonlinear spectroscopies with drastically different information depths on single crystals of the prototypical (CH3NH3)PbI3 methylammonium lead iodide. Two-photon absorption, detected via the resulting generation of carriers and photocurrents (2PI-PC), probes the interband transitions with an information depth in the millimeter range relevant for bulk (single-crystal) material. In contrast, the transient magneto-optical Kerr effect (trMOKE) measured in a reflection geometry determines the excitonic transition energies in the region near (hundreds of nm) the surface which also determine the optical properties in typical thin films. To identify differences between structural phases, we sweep the sample temperature across the orthorhombic-tetragonal phase transition temperature. In the application-relevant room-temperature tetragonal phase (at 170 K), we find a bulk band gap of 1.55 ± 0.01 eV, whereas in the near-surface region excitonic transitions occur at 1.59 ± 0.01 eV. The latter value is consistent with previous reflectance measurements by other groups and considerably higher than the bulk band gap. The small band gap of the bulk material explains the extended infrared absorption of crystalline perovskite solar cells, the low-energy bands which carry optically driven spin-polarized currents, and the narrow bandwidth of crystalline perovskite photodetectors making use of the spectral filtering at the surface.
CRIS-Team Scopus Importer:2020-05-22
Keywords: band gap; CH3NH3PbI3; lead halide perovskite; magneto-optical Kerr effect; nonlinear absorption

Loss analysis on CIGS-modules by using contactless, imaging illuminated lock-in thermography and 2D electrical simulations - Fecher, Frank; Adams, Jens; Vetter, Andreas; Buerhop-Lutz, Claudia; Brabec, Christoph (40th IEEE Photovoltaic Specialist Conference, 2014)
Loss analysis on CIGS-modules are demonstrated by using contactless, imaging illuminated lock-in thermography (ILIT). Power dissipating defects, like shunts, were visualized in commercially manufactured test modules (30 × 30 cm). The evaluations of the ILIT-measurements displayed a correlations with the loss in maximum output power and in open circuit voltage. 2D finite element simulations of the shunts confirmed the correlations. A further simulative parameter study gives a deep understanding of the influence of a shunt on the electrical performance in thin film modules. As ILIT is a contactless and fast method, it has the potential to become a powerful tool for in-line characterization. Furthermore, we consider this technique to be applicable also to other thin film module technologies, like CdTe, a-Si:H or organic photovoltaics.
Keywords: lock-in thermography; module performance; photovoltaic; Pmpp; shunt; Voc

Low-cost copper complexes as p-dopants in solution processable hole transport layers - Kellermann, Renate; Taroata, Dan; Maltenberger, Anna; Hartmann, David; Brabec, Christoph; Schmid, Guenter (Applied Physics Letters, 2015)
We demonstrate the usage of the Lewis-acidic copper(II)hexafluoroacetylacetonate (Cu(hfac)2) and copper(II)trifluoroacetylacetonate (Cu(tfac)2) as low-cost p-dopants for conductivity enhancement of solution processable hole transport layers based on small molecules in organic light emitting diodes (OLEDs). The materials were clearly soluble in mixtures of environmentally friendly anisole and xylene and spin-coated under ambient atmosphere. Enhancements of two and four orders of magnitude, reaching 4.0×10-11 S/cm with a dopant concentration of only 2mol% Cu(hfac)2 and 1.5×10-9 S/cm with 5mol% Cu(tfac)2 in 2,2′,7,7′-tetra(N,N-ditolyl)amino-9,9-spiro-bifluorene (spiro-TTB), respectively, were achieved. Red light emitting diodes were fabricated with reduced driving voltages and enhanced current and power efficiencies (8.6lm/W with Cu(hfac)2 and 5.6lm/W with Cu(tfac)2) compared to the OLED with undoped spiro-TTB (3.9lm/W). The OLED with Cu(hfac)2 doped spiro-TTB showed an over 8 times improved LT50 lifetime of 70h at a starting luminance of 5000cd/m2. The LT50 lifetime of the reference OLED with PEDOT:PSS was only 8h. Both non-optimized OLEDs were operated at similar driving voltage and power efficiency.
Keywords: Engineering controlled terms: Coated materials; Conducting polymers; Copper; Doping (additives); Hole mobility; Light emitting diodes; Organic light emitting diodes (OLED) Ambient atmosphere; Conductivity enhancement; Dopant concentrations; Hole transport layers; Orders of magnitude; Organic light emitting diodes(OLEDs); Reduced driving voltage; Solution processable Engineering main heading: Copper compounds

Low Driving Voltage and High Mobility Ambipolar Field-Effect Transistors with PbS Colloidal Nanocrystals - Bisri, Satria Zulkarnaen; Piliego, Claudia; Yarema, Maksym; Heiß, Wolfgang; Loi, Maria Antonietta (Advanced Materials, 2013)
PbS colloidal nanocrystals (NCs) are promising materials for optoelectronic devices, due to their size-tunable properties. However, there is still minimal understanding of their charge transport mechanism. Through a combination of ligand selections, ambipolar transistor structure optimization, and electrochemical gating usage, high carrier mobility is achieved. The outstanding device characteristics open possibility to investigate the intrinsic transport properties of PbS NCs.
Keywords: colloidal nanocrystals; ambipolar transistor; layer-by-layer assembly; electrolyte gating; metal chalcogenides

Low-temperature and hysteresis-free electron-transporting layers for efficient, regular, and planar structure perovskite solar cells - Hou, Yi; Ramírez Quiroz, César Omar; Scheiner, Simon; Chen, Wei; Stubhan, Tobias; Hirsch, Andreas; Halik, Marcus; Brabec, Christoph (Advanced Energy Materials, 2015)
With the aim of fully utilizing the low processing temperatures of perovskite solar cells, significant progress in replacing high temperature processed TiO by various low-temperature solution processed electron transporting layers (LT-ETLs) was recently reported. Here, recent progress in the development of LT-ETLs for regular planar structure perovskite solar cells, which is essential for achieving high efficiency in parallel to avoiding hysteresis, is reviewed. In addition, the application of a novel hysteresis-free LT-ETLs for regular planar perovskite solar cells in our laboratory is briefly discussed. By incorporating a low temperature processed WOnanoparticular layer in combination with a mixed fullerene functionalized self-assembled monolayers (SAMs), a regular, planar structure, and hysteresis-free perovskite solar cell with a maximum efficiency of almost 15% can be fabricated. Recent progress in the development of low temperature processed electron-transporting layers for regular planar structure perovskite solar cells is reviewed. Moreover, the application of a novel mixed self-assembled monolayers in hysteresis-free perovskite solar cells is briefly discussed. The as-fabricated perovskite solar cells show a maximum efficiency of almost 15%.
Keywords: electron-transporting layers; hysteresis-free solar cells; low-temperature solution processed; perovskite solar cells

Low temperature formation of CuIn1 - xGaxSe2solar cell absorbers by all printed multiple species nanoparticulate Se + Cu-In + Cu-Ga precursors - Möckel, Stefan; Wernicke, Tobias; Arzig, Matthias; Köder, Philipp; Brandl, Marco; Ahmad, Rameez; Distaso, Monica; Peukert, Wolfgang; Hock, Rainer; Wellmann, Peter (Thin Solid Films, 2015)
In this work an all nanoparticulate precursor for application in Cu(InGa)Sesolar cell absorbers is presented. Binary Cu-In nanoparticles, Cu-Ga powder and elemental Se nanoparticles were mixed in dispersion and deposited on Mo-coated substrates. Research was focused on Cu(InGa)Selayer formation kinetics, phase composition characterised by differential scanning calorimetry and in-situ X-ray diffraction (XRD). Furthermore phase composition and morphology were studied by ex-situ XRD, Raman spectroscopy and scanning electron microscopy. The results revealed a fast consumption of the precursor and the formation of CuInSebelow 340 °C. Binary secondary phases were not observed at any temperature.
Keywords: Low-temperature; Copper indium gallium diselenide; Chalcopyrite; Nanoparticulate precursors; In-situ X-ray diffraction; Bimetallic nanoparticles

Low Temperature Photoluminescence of 6H fluorescent SiC - Wei, Yi; Künecke, Ulrike; Jokubavicius, Valdas; Syväjärvi, Mikael; Wellmann, Peter; Ou, Haiyan (E-MRS Spring Meeting 2017, 2017)
We have presented the low temperature photoluminescence (PL) measurements of three 6H fluorescent Silicon Carbide (f-SiC) samples. The epilayers of the f-SiC samples were nitrogenboron co-doped and grown by fast sublimation growth process (FSGP) method on the bulk 6H SiC substrates. The doping concentrations of the f-SiC epilayers were determined by secondary ion mass spectroscopy (SIMS) showing strong n-type, strong p-type and slight p-type extrinsic semiconductor doping of each epilayer. The PL intensity of one commercial 6H bulk SiC (TanKeBlue Ltd.) was also measured and applied as the reference. The PL was excited by a diode laser source with wavelength of 405 nm and power of 5 mW. The temperature of the PL measurement was ranged from 25K to 300K when the liquid nitrogen cryostat was used, while lower temperature from 5K was achieved when the cryostat with liquid helium was applied. The anomalous temperature dependences of the PL intensity spectrum of f-SiC samples were found. The PL peak energy’s S-shape dependence on the temperature was observed which was caused by nitrogen induced localization effect. For strong p-type f-SiC, one more PL intensity peak at 5 k was observed at wavelength of 520 nm, where this extra PL peak was the result of basal plane dislocation and free-to-acceptor recombination.<br
Keywords: SiC; 6H; photoluminescence

Low Temperature Processed Fully Printed Efficient Planar Structure Carbon Electrode Perovskite Solar Cells and Modules - Yang, Fu; Dong, Lirong; Jang, Dongju; Saparov, Begench; Tam, Kai Cheong; Zhang, Kaicheng; Li, Ning; Brabec, Christoph; Egelhaaf, Hans-Joachim (Advanced Energy Materials, 2021)
Scalable deposition processes at low temperature are urgently needed for the commercialization of perovskite solar cells (PSCs) as they can decrease the energy payback time of PSCs technology. In this work, a processing protocol is presented for highly efficient and stable planar n–i–p structure PSCs with carbon as the top electrode (carbon-PSCs) fully printed at fairly low temperature by using cheap materials under ambient conditions, thus meeting the requirements for scalable production on an industrial level. High-quality perovskite layers are achieved by using a combinatorial engineering concept, including solvent engineering, additive engineering, and processing engineering. The optimized carbon-PSCs with all layers including electron transport layer, perovskite, hole transport layer, and carbon electrode which are printed under ambient conditions show efficiencies exceeding 18% with enhanced stability, retaining 100% of their initial efficiency after 5000 h in a humid atmosphere. Finally, large-area perovskite modules are successfully obtained and outstanding performance is shown with an efficiency of 15.3% by optimizing the femtosecond laser parameters for the P2 line patterning. These results represent important progress toward fully printed planar carbon electrode perovskite devices as a promising approach for the scaling up and worldwide application of PSCs.
CRIS-Team Scopus Importer:2021-06-18
Keywords: carbon electrodes; doctor blades; fully printed devices; long-term stability; perovskite solar cells

Low temperature processing of hybrid nanoparticulate Indium Tin Oxide (ITO) polymer layers and application in large scale lighting devices - Maksimenko, Ilja; Wellmann, Peter (Thin Solid Films, 2011)
We report on transparent conductive indium tin oxide (In(2)O(3):Sn; ITO) nanoparticle films processed at a low temperature of 130 degrees C for the application in lighting devices using spin coating and doctor blading techniques. Major emphasis is put on the beneficial application of the particular transparent electrode material for the fabrication of patterned large area electroluminescence lamps. In order to improve film properties like adhesion and conductivity, hybrid nanoparticle-polymer blends out of ITO particles and organic film-forming agent polyvinylpyrrolidone (PVP) and the organofunctional coupling agent 3-methacryloxypropyltrimethoxysilane (MPTS) have been developed. The layers were cured by UV-irradiation, which was also used for lateral structuring of the transparent, conductive electrode. Additional low-temperature heat treatment (T = 130 degrees C) in air and forming gas improved the electronic properties. While pure ITO nanoparticulate layers processed at 130 degrees C exhibited conductance of up to 3.1 Omega(-1) cm(-1), the nanocomposite coatings showed a conductance of up to 9.8 Omega(-1) cm(-1). Corresponding layers with a sheet resistance of 750 Omega/square were applied in electroluminescent lamps. (C) 2011 Elsevier B.V. All rights reserved.
Keywords: TCO (transparent conducting oxide); ITO (indium tin oxide); lighting; electroluminescence lamp

Low-temperature processing of transparent conductive indium tin oxide nanocomposites using polyvinyl derivatives - Maksimenko, Ilja; Wellmann, Peter (Thin Solid Films, 2011)
We report on the influence of additives on the electrical, optical, morphological and mechanical properties of transparent conductive indium tin oxide (In2O3:Sn; ITO) nanoparticle films by the use of polymers as matrix material. Key issues to fabricate layers suitable for use in electronic device applications are presented. Polyvinyl derivatives polyvinyl acetate, polyvinyl alcohol (PVA) and polyvinyl butyral were applied and their suitability to form transparent conductive ITO nanocomposite coatings at a maximum process temperature of 130 degrees C was investigated. A low-temperature treatment with UV-light has been developed to provide the possibility of curing ITO thin films deposited on substrates which do not withstand high process temperatures. Compared to best pure ITO layers (0.2 Omega(-1) cm(-1)), the ITO-PVA nanocomposite coatings show a conductance value of 4.1 Omega(-1) cm(-1) and 5.9 Omega(-1) cm(-1) after reducing in forming gas. Sheet resistance of ca. 1200 Omega/square with coexistent transmittance of 85% at 550 nm for a layer thickness of about 1.45 mu m was achieved. The conductance enhancement is a consequence of nanoparticulate ITO network densification due to the acting shrinkage forces caused by the polymer matrix during film drying and additionally UV-induced crosslinking of PVA. (C) 2011 Elsevier B. V. All rights reserved.
Keywords: Indium tin oxide (ITO); Nanoparticles; Polyvinyl alcohol (PVA); Polyvinyl acetate (PVAc); Polyvinyl butyral (PVB); Nanocomposite

Low-Temperature Solution-Processed Kesterite Solar Cell Based on in Situ Deposition of Ultrathin Absorber Layer - Hou, Yi; Azimi, Seyed Hamed; Gasparini, Nicola; Savador, Michael; Chen, Wei; Khanzada, Laraib Sarfraz; Brandl, Marco; Hock, Rainer; Brabec, Christoph (ACS Applied Materials and Interfaces, 2015)
The production of high-performance, solution-processed kesterite Cu2ZnSn(Sx,Se1-x)4 (CZTSSe) solar cells typically relies on high-temperature crystallization processes in chalcogen-containing atmosphere and often on the use of environmentally harmful solvents, which could hinder the widespread adoption of this technology. We report a method for processing selenium free Cu2ZnSnS4 (CZTS) solar cells based on a short annealing step at temperatures as low as 350 °C using a molecular based precursor, fully avoiding highly toxic solvents and high-temperature sulfurization. We show that a simple device structure consisting of ITO/CZTS/CdS/Al and comprising an extremely thin absorber layer (∼110 nm) achieves a current density of 8.6 mA/cm2. Over the course of 400 days under ambient conditions encapsulated devices retain close to 100% of their original efficiency. Using impedance spectroscopy and photoinduced charge carrier extraction by linearly increasing voltage (photo-CELIV), we demonstrate that reduced charge carrier mobility is one limiting parameter of low-temperature CZTS photovoltaics. These results may inform less energy demanding strategies for the production of CZTS optoelectronic layers compatible with large-scale processing techniques.
Keywords: CZTS; device stability; kesterite solar cells; low-temperature processing; molecular based precursor

Low temperature, solution processed metal oxide buffer layers fulfilling large area production requirements - Stubhan, Tobias; Litzov, Ivan; Li, Ning; Wang, Hao; Krantz, Johannes; Machui, Florian; Steidl, M.; Oh, H.; Matt, Gebhard; Brabec, Christoph (Proceedings of SPIE, 2012)
This paper is a review of our previous work on the field of low temperature, solution processed metal oxide buffer layers published in various journals. Our work focuses on zinc oxide (ZnO) and aluminum-doped zinc oxide (AZO) as n-type and molybdenum oxide (MoO3) as p-type solution processed buffer layer. In addition to that, we investigate the surface modification of AZO using phosphonic acid-anchored aliphatic and fullerene self assembled monolayers (SAMs
Keywords: Aluminum-doped zinc oxide; Low temperatures; Metal oxides; P-type; Phosphonic; Production requirements; Solution-processed; Zinc oxide (ZnO) Engineering controlled terms: Aluminum; Metallic compounds; Molybdenum oxide; Optical waveguides; Organic acids; Self assembled monolayers; Temperature; Zinc oxide Engineering main heading: Buffer layers

Low-threshold amplified spontaneous emission and lasing from colloidal nanocrystals of caesium lead halide perovskites - Yakunin, Sergii; Protesescu, Loredana; Krieg, Franziska; Bodnarchuk, Maryna I.; Nedelcu, Georgian; Humer, Markus; De Luca, Gabriele; Fiebig, Manfred; Heiß, Wolfgang; Kovalenko, Maksym V. (Nature Communications, 2015)
Metal halide semiconductors with perovskite crystal structures have recently emerged as highly promising optoelectronic materials. Despite the recent surge of reports on microcrystalline, thin-film and bulk single-crystalline metal halides, very little is known about the photophysics of metal halides in the form of uniform, size-tunable nanocrystals. Here we report low-threshold amplified spontaneous emission and lasing from B10nm monodisperse colloidal nanocrystals of caesium lead halide perovskites CsPbX3 (X=Cl, Br or I, or mixed Cl/Br and Br/I systems). We find that room-temperature optical amplification can be obtained in the entire visible spectral range (440-700 nm) with low pump thresholds down to 5±1 μJ cm-2 and high values of modal net gain of at least 450±30 cm-1. Two kinds of lasing modes are successfully observed: whispering-gallery-mode lasing using silica microspheres as high-finesse resonators, conformally coated with CsPbX3 nanocrystals and random lasing in films of CsPbX3 nanocrystals.
Keywords: EMTREE drug terms: cesiumcolloidal nanocrystalhalideleadmicrospherenanocrystalperovskitesilicon dioxideunclassified drug GEOBASE Subject Index: cesiumcolloidcrystal structureleadnanotechnologyperovskitethreshold EMTREE medical terms: Articleopticsroom temperature

LPE growth of Tb3Al5O12:Ce single crystalline film converters for WLED application - Markovskyi, A.; Gorbenko, V.; Zorenko, T.; Yokosawa, Tadahiro; Will, Johannes; Spiecker, Erdmann; Batentschuk, Miroslaw; Elia, Jack; Fedorov, A.; Zorenko, Yu. (CrystEngComm, 2021)
The possibility of development of an efficient phosphor converters (PC) for white LED (WLED) based on single crystalline films (SCF) of Ce3+ doped Tb3Al5O12 garnet (TbAG:Ce), grown using liquid-phase epitaxy method onto Y3Al5O12 (YAG) substrates, is evidenced for the first time in this work. The detail investigation of the structural properties of the TbAG:Ce SCF/YAG epitaxial structures was performed. High-resolution scanning transmission electron microscopy and composition analysis revealed an interface with high structural quality including the formation of a transition layer with a 5-7 nm thickness between TAG:Ce SCF and YAG substrate. The transition layer consisted of solid solutions between Tb3Al5O12:Ce and Y3Al5O12 garnets gradually changing from undoped YAG in substrate towards TbAG:Ce in the film and allowed to reduce the mismatch-stress. The absorption, cathodoluminescence, photoluminescence properties of TbAG:Ce SCFs were investigated as well. Furthermore, the dependence of photoconversion properties on the film thicknesses was studied to construct the prototype of efficient warm white LEDs. The change in the crystal thickness enabled tuning of the white light tons from cold white/daylight to neutral white. These results can be useful for the development of a novel generation of phosphor converters for white LEDs.
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Luminescence Analysis of PV-Module Soiling in Germany - Doll, Bernd; Forberich, Karen; Hepp, Johannes; Langner, Stefan; Buerhop-Lutz, Claudia; Hauch, Jens; Brabec, Christoph; Peters, Ian Marius (IEEE Journal of Photovoltaics, 2021)
Energy losses of photovoltaic (PV) plants because of soiling are a problem in all regions, including Germany. Soft soiling, caused by a uniform dust film, is shading a PV module and is reducing yield depending on the thickness of the debris layer. Hard soiling, caused by agglomerations of dust or dirt, only covers parts of a PV module, and it causes local shading. A spot check of modules from different PV power plants in Germany revealed a power reduction because of soft- and hard soiling of up to 6%. Determination of soiling type and amount is a prerequisite for decisions about cleaning and for optimizing yield. In this article, we show that luminescence imaging can be used to detect and characterize soiling and quantify losses. For this purpose, we compare luminescence images before and after cleaning and we show that soiling becomes detectable and power losses quantifiable from difference images. We also show that the impact of hard soiling can be quantified from a single photoluminescence (PL) image. This technique may enable a fully automated quantification of power losses because of hard soiling in PV- modules and strings in the future.
CRIS-Team WoS Importer:2021-12-31

Luminescence of Ce3+ multicenters in Ca2+-Mg2+-Si4+ based garnet phosphors - Gorbenko, V.; Zorenko, T.; Witkiewicz, S.; Paprocki, K.; Iskaliyeva, A.; Kaczmarek, A. M.; Van Deun, R.; Khaidukov, M. N.; Batentschuk, Miroslaw; Zorenko, Yu (Journal of Luminescence, 2018)
Comparison of the luminescent properties of Ca3Sc2Si3O12:Ce and Ca2YMgScSi3O12:Ce single crystalline films (SCF) phosphors, grown by the liquid phase epitaxy method, was performed in this work. We have observed formation of the Ce3+ multicenters in Ca3Sc2Si3O12:Ce and Ca2YMgScSi3O12:Ce in the emission and excitation spectra as well as in the decay kinetics of the Ce3+ luminescence in SCFs of these garnets. Such Ce3+ multicenters possess different crystal field strength due to the inhomogeneous local surroundings of the dodecahedral positions of garnet host at the substitution of the octahedral positions by hetero-valence Mg2+ and Sc3+ ions and the tetrahedral positions by Si4+ ions. We confirm the presence of an effective energy transfer between different Ce3+ multicenters in Ce3+ doped Ca3Sc2Si3O12 and Ca2YMgScSi3O12 garnets. The positive trends in variations of the spectroscopic properties of the Ca2YMgScSi3O12:Ce garnet with respect to Ca3Sc2Si3O12:Ce garnet were observed also due to substitution of the dodecahedral sites of the garnet host by Y3+ ions and the octahedral sites by Mg2+ ions, which can be suitable for the development of new converters of white LEDs. Namely, due to the Y3+-Mg2+ doping, the luminescence spectrum of Ce3+ ions in Ca2YMgScSi3O12:Ce SCFs significantly extends in the red range in comparison with the Ca3Sc2Si3O12:Ce SCF counterpart. © 2018 Elsevier B.
Keywords: LED converters; Luminescence; Ca2+-Mg2+-Si4+ based garnets; Ce3+ dopant; Single crystalline films

Luminescence of Mn2+ ions in Tb3Al5O12 garnet - Zorenko, Yu; Gorbenko, V.; Voznyak, Taras; Batentschuk, Miroslaw; Osvet, Andres; Winnacker, Albrecht (Journal of Luminescence, 2010)
The paper is dedicated to investigation of the Mn2+ luminescence in Tb_3Al5O12 (TbAG) garnet, as well as the processes of excitation energy transfer between host cations (Tb3+ ions) and activators (Mn2+ and Mn2+–Ce3+ pair ions) in single crystalline films of TbAG:Mn and TbAG:Mn,Ce garnets which can be considered as promising luminescent materials for conversion of LED's radiation. Due to the effective energy transfer between TbAG host and activator, Mn2+ ions in TbAG possess the bright orange luminescence in the bands peaked at 595 nm with a lifetime of 0.64 ms which are caused by the ^4T1i̊ghtarrow6A1 radiative transitions. The simultaneous process of energy transfer is realized in TbAG:Mn,Ce: (i) from Tb3+ to Mn2+ ions; (ii) from Tb3+ cations to Ce3+ ions and then partly to Mn2+ ions through Tb3+ ion sublattice and Ce–Mn dipole–dipole interaction.
Keywords: Single crystalline films; TbAG; Energy transfer; Mn2+ and Ce3+ dopants; Luminescence

Luminescence properties and energy transfer processes in YAG:Yb,Er single crystalline films - Zorenko, Yu; Gorbenko, V.; Savchyn, V.; Batentschuk, Miroslaw; Osvet, Andres; Brabec, Christoph (Radiation Measurements, 2013)
The paper is dedicated to the study of the optical properties of YAG:Yb,Er single-crystalline films (SCF) grown by liquid phase epitaxy. The absorption, cathodoluminescence and time-resolved photoluminescence spectra and photoluminescence decay curves were measured for the SCFs with different doping levels of Er (from 0.6 to 4.2 at.%) and Yb (from 0.1 to 0.6 at.%). The spectra, excited by synchrotron radiation in the fundamental absorption range of the YAG and in the intraionic absorption bands of both dopants, reveal energy transfer from the YAG host to the Er and Yb ions and between these ions. © 2013 Elsevier Ltd. All rights reserved.
Keywords: Er 3+ and Yb3+ dopants; Liquid phase epitaxy; Luminescence; Single crystalline films; YAG

Luminescence properties of Yb3+-Tb3+ co-doped amorphous silicon oxycarbide thin films - Flores, Loreleyn F.; Tucto, Karem Y.; Guerra, Jorge A.; Töfflinger, Jan A.; Serquen, Erick S.; Osvet, Andres; Batentschuk, Miroslaw; Winnacker, Albrecht; Grieseler, Rolf; Weingärtner, Roland (Optical Materials, 2019)
This work analyzes the photoluminescence emission of Yb 3+ and Tb 3+ ions in co-doped silicon oxycarbide thin films, their activation by thermal treatment, and reveals their luminescent properties regarding the energy transfer between them. Three samples of silicon oxycarbide were prepared by rf magnetron sputtering from SiC, Yb and Tb targets in an oxygen/argon atmosphere. The first one is the undoped silicon oxycarbide sample, the second one is Tb single doped, and the last one is the Yb-Tb co-doped sample. All three samples are identified as silicon oxycarbides with a low carbon content using energy dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy. The latter shows the presence of the vibrational modes of Si–C and Si–O bonds. Subsequent annealing treatments up to temperatures of 750 °C led to the rare earths optical activation in the samples. For each annealing step, we present the photoluminescence spectra using an above-bandgap excitation of 325 nm. The Tb 3+ and Yb 3+ -related luminescence lines were identified. The Yb 3+ ions luminescence for the co-doped sample shows concentration quenching above annealing temperatures of 500 °C whereas the Tb 3+ ions luminescence intensity remains almost constant. The analysis of the photoluminescence excitation spectra shows the direct excitation of the Tb 3+ ions in the Tb-doped samples. A high suppression of the direct excitation of the Tb 3+ ions in the Yb-Tb co-doped samples was observed. The energy transfer from Tb 3+ to Yb 3+ ions in co-doped samples is evidenced, first, by the decrease of the Tb 3+ photoluminescence intensity in the co-doped compared to the Tb doped sample. Second, a change from nearly single exponential to nonexponential decay in the Tb 3+ photoluminescence decay curves and third, by the reduction of the Tb 3+ decay time from 1.2 ms in the Tb-doped sample to 0.5 ms in the Yb-Tb co-doped sample.
CRIS-Team Scopus Importer:2019-05-16
Keywords: Photoluminescence lifetime; rf magnetron sputtering; Silicon oxycarbide; Terbium; Ytterbium

Luminescent and scintillation properties of Ce3+ doped Ca2RMgScSi3O12 (R = Y, Lu) single crystalline films - Gorbenko, V.; Zorenko, T.; Pawlowski, P.; Iskaliyeva, A.; Paprocki, K.; Suchocki, A.; Zhydachevskii, Ya.; Fedorov, A.; Khaidukov, Nicholas; Van Deun, R.; Schroeppel, F.; Osvet, Andres; et al. (Journal of Luminescence, 2018)
The work is dedicated to the growth and investigation of the luminescent and scintillation properties of single crystalline films (SCFs) of Ca2−xR1+xMg1+xSc1−xSi3O12:Ce (R = Y, Lu) mixed garnets with x = 0–0.25, grown using the liquid phase epitaxy method onto Y3Al5O12 substrates from PbO-B2O3 based flux. The absorption, luminescent and scintillation properties of Ca2−xY1+x Mg1+xSc1−xSi3O12:Ce and Ca2−xLu1+xMg1+xSc1−xSi3O12:Ce SCFs with x = 0 and 0.25 were investigated and compared with the reference YAG:Ce and LuAG:Ce SCFs. Using the Ca2+, Mg2+ and Si4+ alloying, the Ce3+ emission spectra in Ca2−xR1+xMg1+xSc1−xSi3O12:Ce (R = Y, Lu; x = 0–0.25) SCFs can be notably extended in the red range in comparison with YAG:Ce and LuAG:Ce SCFs due to the increase of crystal field strength and Ce3+ multicenter creation in the dodecahedral positions of the lattices of these mixed garnet compounds. Due to the formation of Ce4+ ions, the as-grown Ca2−x R1+xMg1+xSc1−xSi3O12:Ce (R = Y, Lu) SCFs at x = 0 and 0.25 show relatively low light yield. However, after annealing in reducing atmosphere (95% N2 + 5% H2) at T > 1000 °C, a recharging Ce4+→Ce3+ takes place. After that, these SCFs possess the light yield about of 30% and 31% in comparison with the reference YAG:Ce and LuAG:Ce SCFs, respectively, and a fast scintillation response with the decay times in the ns range under α–particles excitation by 239Pu (5.15 MeV) sourc
Keywords: Single crystalline films; Scintillators; Liquid phase epitaxy; Ce dopant; Garnets

Luminescent down-shifting layers with Eu2+ and Eu3+ doped strontium compound particles for photovoltaics - Solodovnyk, Anastasiia; Hollmann, Andre; Osvet, Andres; Forberich, Karen; Stern, Edda; Batentschuk, Miroslaw; Klupp Taylor, Robin; Brabec, Christoph (Next Generation Technologies for Solar Energy Conversion V, 2014)
In this contribution we discuss luminescent down-shifting (LDS) systems consisting of a polymer matrix filled with phosphor particles. It is an elegant approach to make a use of potentially destructive or otherwise wasted high energy photons and diminish charge carrier losses caused by thermalization in photovoltaics. Sub-micron and micron sized particles of strontium aluminate doped with Eu2+ and strontium carbonate doped with Eu3+ ions are chosen for the application due to their suitable absorption in UV spectral region. These particles exhibit strong luminescence in the visible range between 520 and 650 nm. The systems are carefully designed to meet critical optical requirements such as high transparency in the visible spectrum as well as sufficient absorption of UV light. They are coated on quartz glass substrates (20 x 20 x 1 mm) and can be easily laminated to different kinds of solar cells without any modification to well-established device fabrication processes. Optical characterization further confirms that particles of a few microns in size generate strong light scattering in layers due to the sizes slightly larger than visible light wavelengths. Dried thick layers of 20 to 100 μm are tested with CIGS and organic cells. The concept of light conversion is experimentally proven. However, optical losses cause a reduction in the overall performance of the tested devices. Possible ways to bring down the amount of light scattering and, thus, to increase optical transmission for the studied system are also addressed, and are a subject of future research.
Keywords: Light absorption; Light scattering; Luminescent down-shifting; Phosphor particles; Polymer matrix; Solar cell; Solution processed layers

Luminescent properties and energy transfer processes in YAG:Er single crystalline films - Zorenko, Yu.; Gorbenko, V.; Zorenko, T.; Savchyn, V.; Batentschuk, Miroslaw; Osvet, Andres; Brabec, Christoph (Journal of Luminescence, 2014)
The paper is dedicated to studying the optical properties of YAG:Er single crystalline films (SCF) grown by liquid phase epitaxy. The absorption, cathodoluminescence and photoluminescence spectra were measured for the YAG:Er SCFs with different doping levels of Er from 0.735 to 6.6 at%. The luminescence spectra and luminescence excitation spectra under synchrotron radiation excitation in the fundamental absorption range of the YAG and in the intrinsic f-d absorption bands of Er ions reveal the peculiarities of energy transfer from the YAG host to the Er ions. © 2014 Elsevier B.V.
Keywords: Liquid phase epitaxy; Luminescence; Single crystalline films; YAG

Luminescent properties of Ce3+ doped LiLuP4O12 tetraphosphate under synchrotron radiation excitation - Zorenko, T.; Paprocki, K.; Levchuk, Ievgen; Batentschuk, Miroslaw; Epelbaum, B.; Fedorov, A.; Zorenko, Yu (Journal of Luminescence, 2019)
The work is dedicated to the investigation of the luminescent and scintillation properties of the LiLuP4O12:Ce tetraphosphate, as a new scintillation material. The LiLuP4O12:Ce polycrystalline samples were grown by the Micropulling down (MPD) method. Under e-beam excitation and excitation with energy above the band gap of host, the LiLuP4O12:Ce crystals possess very strong Ce3+ luminescence in the UV range in the bands peaked at 334 and 355 nm with a lifetime of 23 ns at room temperature. We have found that the scintillation light yield (LY) of polished plates prepared from MPD grown LiLuP4O12:Ce samples is relatively high and comparable with the LY of reference BGO crystal. Future improvement of the scintillation LY is expected at the optimization of the growth conditions of this compound. The energy structure of Ce3+ ions, related to the 4f-5d transitions of Ce3+ ions in the 3.7-25 eV range, was determined from the excitation and emission spectra of LiLuP4O12:Ce crystal under excitation by synchrotron radiation. We have also determined the energy of creation of excitons bound with Ce3+ ions and estimated the energy gap in LiLuP4O12 host, which is equal to 8.5 and > 9.0 eV, respectively.
CRIS-Team WoS Importer:2019-04-12

Luminescent properties of LuAG:Yb and YAG:Yb single crystalline films grown by Liquid Phase Epitaxy method - Zorenko, Yu; Zorenko, T.; Gorbenko, V.; Voznyak, T.; Popielarski, P.; Batentschuk, Miroslaw; Osvet, Andres; Brabec, Christoph; Kolobanov, V.; Spasky, D.; Fedorov, A. (Elsevier, 2016)
In this work, investigation of the spectroscopic parameters of the luminescence of Yb3+ ions in single crystalline films of Lu3Al5O12 and Y3Al5O12 garnets was performed using the synchrotron radiation excitation with the energy in the range of Yb3+ charge transitions (CT), exciton range and the onset of interband transitions of these garnets. The basic spectroscopic parameters of the Yb3+ CT luminescence in LuAG and YAG hosts were determined and summarized with taking into account the differences in the band gap structure of these garnets. (C) 2016 Elsevier Ltd. All rights reserved.
Keywords: Luminescence; Liquid phase epitaxy; Single crystalline film; YAG and LuAG garnets; Yb dopant

Luminescent Properties of Nanopowder and Single-Crystalline Films of TbAG:Ce Garnet - Bolek, Paulina; Zeler, Justyna; Gorbenko, Vitalii; Zorenko, Tetiana; Popielarski, Pawel; Bartosiewicz, Karol; Osvet, Andres; Batentschuk, Miroslaw; Zych, Eugeniusz; Zorenko, Yuriy (physica status solidi (b), 2020)
Herein, the luminescence properties of nanopowders (NPs), thin NP film and single-crystalline film (SCF) of TbAG:Ce garnet are compared. The NPs are prepared by the combustion synthesis. NP films with thickness of 300 nm are prepared using the spin-coating method. SCFs are grown by liquid phase epitaxy. Structure and morphology of NPs, NP films, and SCFs are studied using scanning electron microscopy and X-ray diffraction. The luminescence properties of these samples are characterized by cathodoluminescence (CL) and photoluminescence (PL). CL spectra of the TbAG:Ce NP, NP films, and SCFs show the dominant Ce3+ emission in the garnet host. Meanwhile, in the PL spectra of NPs, the complex UV emission band is also observed. Its origin is related to 1) thermodynamic instability of TbAG garnet phase and formation of TbAP:Ce perovskite phase under conditions of NP preparation; 2) formation of UV emitting centers in both TbAG and TbAP hosts. This UV emission band is fully absent in TbAG:Ce SCF. Therefore, TbAG SCFs are useful objects for studying the luminescence of this garnet and different dopants in them. Furthermore, both TbAG:Ce NP films and SCFs are applicable for producing cathodoluminescent and scintillating screens with thickness in the μm/sub μm ranges.
CRIS-Team Scopus Importer:2020-02-28
Keywords: Ce; luminescence; nanopowder films; nanopowders; single-crystalline films; TbAG garnets

Machine Learning for Ultra High Throughput Screening of Organic Solar Cells: Solving the Needle in the Haystack Problem - Hußner, Markus; Pacalaj, Richard Adam; Olaf Müller-Dieckert, Gerhard; Liu, Chao; Zhou, Zhisheng; Majeed, Nahdia; Greedy, Steve; Ramirez, Ivan; Li, Ning; Hosseini, Seyed Mehrdad; Uhrich, Christian; Brabec, Christoph; et al. (Advanced Energy Materials, 2024)
Over the last two decades the organic solar cell community has synthesized tens of thousands of novel polymers and small molecules in the search for an optimum light harvesting material. These materials are often crudely evaluated simply by measuring the current–voltage (JV) curves in the light to obtain power conversion efficiencies (PCEs). Materials with low PCEs are quickly disregarded in the search for higher efficiencies. More complex measurements such as frequency/time domain characterization that could explain why the material performed as it is often not performed as they are too time consuming/complex. This limited feedback forced the field to advance using a more or less random walk of material development and has significantly slowed progress. Herein, a simple technique based on machine learning that can quickly and accurately extract recombination time constants and charge carrier mobilities as a function of light intensity simply from light/dark JV curves alone. This technique reduces the time to fully analyze a working cell from weeks to seconds and opens up the possibility of not only fully characterizing new devices as they are fabricated, but also data mining historical data sets for promising materials the community has overlooked.
CRIS-Team Scopus Importer:2024-01-26
Keywords: drift diffusion; machine learning; organic photovoltaic; solar

Managing Phase Orientation and Crystallinity of Printed Dion-Jacobson 2D Perovskite Layers via Controlling Crystallization Kinetics - Chen, Yijun; Hu, Jinlong; Xu, Zhenhua; Jiang, Zhengyan; Chen, Shi; Xu, Baomin; Xiao, Xiudi; Liu, Xianhu; Forberich, Karen; Brabec, Christoph; Mai, Yaohua; Guo, Fei (Advanced Functional Materials, 2022)
Two-dimensional perovskites have attracted substantial attention for solar cell applications because of their higher stability as compared to their 3D analogs. To achieve efficient charge transport in thin-film devices, obtaining high crystalline perovskite crystals perpendicularly aligned to the substrate is of great importance. This article reports the scalable printing of high-quality Dion-Jacobson (DJ) perovskite thin films via tailoring crystallization kinetics. Introducing a small amount of 1-methyl-2-pyrrolidinone to the conventional N,N-dimethylformamide:dimethyl sulfoxide-based precursor, the strong coordination with ammonium spacers enables a notably retarded crystallization, which results in perovskite films with distinctly enhanced crystallinity, highly vertical orientation, and graded phase distribution. Accordingly, efficient charge generation and ultrafast interphase charge transfer are realized. The champion DJ perovskite device delivers a high current density of 17.10 mA cm(-2), an impressive open-circuit voltage of 1.21 V, leading to a stabilized efficiency of 16.19%. In addition, the devices processed from the ternary solvent exhibit remarkably improved stability under stimuli with light, heat, and humidity, benefiting from their superb phase stability. This work demonstrates an important advancement in scalable deposition of DJ perovskite thin films for efficient and stable photovoltaic devices.
CRIS-Team WoS Importer:2022-02-18

Material Properties of Laser-Welded Thin Silicon Foils - Hessmann, M. T.; Kunz, T.; Voigt, M.; Cvecek, K.; Schmidt, Michael; Bochmann, A.; Christiansen, S.; Auer, R.; Brabec, Christoph (International Journal of Photoenergy, 2013)
An extended monocrystalline silicon base foil offers a great opportunity to combine low-cost production with high efficiency silicon solar cells on a large scale. By overcoming the area restriction of ingot-based monocrystalline silicon wafer production, costs could be decreased to thin film solar cell range. The extended monocrystalline silicon base foil consists of several individual thin silicon wafers which are welded together. A comparison of three different approaches to weld 50 mu m thin silicon foils is investigated here: (1) laser spot welding with low constant feed speed, (2) laser line welding, and (3) keyhole welding. Cross-sections are prepared and analyzed by electron backscatter diffraction (EBSD) to reveal changes in the crystal structure at the welding side after laser irradiation. The treatment leads to the appearance of new grains and boundaries. The induced internal stress, using the three different laser welding processes, was investigated by micro-Raman analysis. We conclude that the keyhole welding process is the most favorable to produce thin silicon foil

Materials-Related Solutions for Industry - Wellmann, Peter (Materials Innovation for the global circular economy and sustainable society, 2017)
The purpose of the Sixth World Materials Summit, as was true of its five predecessors, is to bring together policy- and decision-makers, experts in markets and industrial technologies, and leaders from the science research community. They assess the status of the many global challenges we face today, identify the best paths forward, and recommend actions that will get us moving along those paths. This year’s program focuses on Materials Innovation for the Global Circular Economy and Sustainable Society. The economic model that focuses on eliminating waste and inefficiency and promotes greater resource productivity — what we call the ‘circular economy’—has been discussed in many forums. Sustainability is part and parcel of that concept. Today’s key materials provision, materials processing and materials application sustainability issues can be seen in the example of personal mobility applications.There are four significant elements in the system chain: (1) renewable energy conversion, (2) flexible power plants to level the time dependence of the electric power supply, (3) sharing energy using electric grids, and (4) handling the major challenge of energy storage on various time scales. In all cases, materials play an important role, and materials modelling using computer simulation has the potential to enhance system efficiency as well as operation lifetime.<br
Keywords: Renewable energy conversion; electric power supply; electric grids; energy storage; materials Innovation; sustainability

Material Strategies to Accelerate OPV Technology Toward a GW Technology - Brabec, Christoph; Distler, Andreas; Du, Xiaoyan; Egelhaaf, Hans-Joachim; Hauch, Jens; Heumüller, Thomas; Li, Ning (Advanced Energy Materials, 2020)
With the rise of the solar power century, photovoltaic applications and installations will go beyond the traditional green field power plants and enter any aspect of daily life. Organic photovoltaics (OPVs) demonstrate certified cell efficiencies of over 17% and are expected to contribute to versatile applications powered by solar energy, for instance, applications rely on flexibility, transparency, color management, or integrability. In this work, the progress of OPV technology is briefly reviewed and the material strategies to accelerate OPV technology toward a GW era are analyzed. In addition to the exciting efficiency values achieved for small area devices, there are many important criteria deciding the success of OPV technology. By taking into consideration the synthetic complexity of OPV materials and the operational stability of OPV devices, the industrial figure of merit (i-FoM) is proposed as a fast and reliable method to verify the true potential of a novel material. Furthermore, “soft” key performance indicators are introduced, such as toxicity, flexibility, transparency, processing, which require different development strategies to reflect the potential of OPV technology for specific applications.
CRIS-Team Scopus Importer:2020-10-09
Keywords: device operational stability; organic photovoltaics; organic solar modules; synthetic complexity

Maximizing concentrated solar power (CSP) plant overall efficiencies by using spectral selective absorbers at optimal operation temperatures - Burlafinger, Klaus; Vetter, Andreas; Brabec, Christoph (Solar Energy, 2015)
Selective absorbers for CSP plants to suppress thermal losses and to increase the efficiency is a promising topic and strong scientific efforts have been spent on how to design and realize such materials. However, there has been no comprehensive optimization analysis of the overall efficiency of CSP plants with selective absorbers.We performed a comprehensive computational parameter study of operation temperature and optical properties of the absorber and investigated their effect on the overall plant efficiency in dependence of sun light concentration up to C=2000 suns. Optimal operation temperatures were shown not to exceed 1383. K. By using selective absorbers instead of a black body or currently used materials, our assessment yields a potential electrical power output gain of up to around 35%. Our investigations also provide the optical parameters of an ideal (perfect selective) absorber. Its optimal cut off wavelength λcut lies around 2.4. μm for concentration factors below 120 and above 600 suns. For C in the range of 120-600 suns the value of the cut off wavelength is 1.79. μm. Simulating non-ideal (realistic) absorption properties, it was found that the strongest influence is caused by high absorption at low wavelengths. Low emittance at longer wavelengths plays a less important role. Also the sharpness of the transition from high absorption to low emittance plays a minor role regarding overall plant efficiency. As a rule of thumb, the cut-off wavelength should be at around 2.4. μm when assuming realistic (non-ideal) spectral selectivity. Finally, the theoretical maximum overall efficiency of a CSP plant achievable by an ideal selective absorber was calculated to up to 73% at 2000 suns and even up to 65% for a selective absorber with realistic optical properties.
Keywords: Absorber; CSP; Optimal operation temperature; Overall efficiency; Selective; Spectral

Maximizing Performance and Stability of Organic Solar Cells at Low Driving Force for Charge Separation - Lüer, Larry; Wang, Rong; Liu, Chao; Dube, Henry; Heumüller, Thomas; Hauch, Jens; Brabec, Christoph (Advanced Science, 2023)
Thanks to the development of novel electron acceptor materials, the power conversion efficiencies (PCE) of organic photovoltaic (OPV) devices are now approaching 20%. Further improvement of PCE is complicated by the need for a driving force to split strongly bound excitons into free charges, causing voltage losses. This review discusses recent approaches to finding efficient OPV systems with minimal driving force, combining near unity quantum efficiency (maximum short circuit currents) with optimal energy efficiency (maximum open circuit voltages). The authors discuss apparently contradicting results on the amount of exciton binding in recent literature, and approaches to harmonize the findings. A comprehensive view is then presented on motifs providing a driving force for charge separation, namely hybridization at the donor:acceptor interface and polarization effects in the bulk, of which quadrupole moments (electrostatics) play a leading role. Apart from controlling the energies of the involved states, these motifs also control the dynamics of recombination processes, which are essential to avoid voltage and fill factor losses. Importantly, all motifs are shown to depend on both molecular structure and process conditions. The resulting high dimensional search space advocates for high throughput (HT) workflows. The final part of the review presents recent HT studies finding consolidated structure–property relationships in OPV films and devices from various deposition methods, from research to industrial upscaling.
CRIS-Team Scopus Importer:2023-12-15
Keywords: electrostatics; exciton binding energy; high throughput methods; hybridization; open circuit voltage losses; organic photovoltaics

Mechanical and Electrical Failure of Silver Nanowire Electrodes: A Scale Bridging In Situ Electron Microscopy Study - Schrenker, Nadine; Schweizer, Peter; Moninger, Marco; Karpstein, Nicolas; Mackovic, Mirza; Spyropoulos, Georgios; Göbelt, Manuela; Christiansen, Silke; Brabec, Christoph; Spiecker, Erdmann (Microscopy and Microanalysis, 2019)

Mechanical Failure of Transparent Flexible Silver Nanowire Networks for Solar Cells using 3D X-Ray Nano Tomography and Electron Microscopy - Englisch, Silvan; Wirth, Janis; Schrenker, Nadine; Tam, Kai Cheong; Egelhaaf, Hans-Joachim; Brabec, Christoph; Spiecker, Erdmann (Microscopy and Microanalysis, 2018)

Mechanisms of high-temperature corrosion in helium containing small amounts of impurities. II. Corrosion of the nickel-base alloy inconel 617 - Christ, Hans-Jürgen; Künecke, Ulrike; Meyer, K; Sockel, Hans-Georg (Oxidation of Metals, 1988)
Application of the technical nickel-base alloy IN 617 in the primary circuit of the high-temperature gas-cooled reactor is limited essentially by the chemical reactions with the impurities (CO, CO2, H2, CH4, H2O) in the helium coolant. The interactions of the alloy with the reactive impurities in different helium-base gases were investigated by thermogravimetry in a gas-tight microbalance and by simultaneous measurement of the changes in gas composition by a continuous sensitive mass spectrometric analysis. The results demonstrate that the set of six reaction equations deduced in part 1 can be applied to describe the corrosion of the alloy. The occurrence of the various reactions is determined essentially by temperature. For the case of a standardized helium gas (HHT-He), three temperature regions can be distinguished. Below a critical temperature (about 1105 K), the presence of CO can cause simultaneous oxidation and carburization. Above this temperature, this reaction does not reverse itself. Rather, oxidation by CO2 and H2O takes place that shows, after a transient period, the same kinetics observed in undiluted oxygen-containing gases. At temperatures above about 1205 K, decarburization of the alloy accompanied by the production of CO takes place, leading to severe destruction of the carbide microstructure and, therefore, limiting the applicability of the materia
Keywords: decarburization; carburization; mechanisms; kinetics; oxidation; Ni-base alloy IN 617; reactor helium

Mechanochemical Synthesis of Cesium Titanium Halide Perovskites Cs2TiBr6-xIx (x=0, 2, 4, 6) - Kupfer, Christian; Elia, Jack; Kato, Masashi; Osvet, Andres; Brabec, Christoph (Crystal Research and Technology, 2022)
Perovskite materials have a great variety of applications, such as X-ray detection, lasing and piezoelectric, or solar energy harvesting. While achieving record efficiencies, perovskite solar cells suffer from the presence of toxic lead in their crystal structure. One possibility to circumvent this issue is via the family of vacancy-ordered double-perovskites, where lead atoms are replaced alternatingly by a tetravalent atom and a vacant lattice site. From this material family, Cs2TiBr6 has recently emerged as a promising candidate due to its favorable reported properties for photovoltaic applications specifically. This paper presents a novel and facile synthesis route to obtain phase-pure Cs2TiBr6 and its lesser-studied iodine-based relatives Cs2TiBr4I2, Cs2TiBr2I4, and Cs2TiI6 via high-energy mechanochemical ball milling. The materials are characterized with structural, microscopic, and photophysical techniques to reveal indirect bandgaps with values of 1.88, 1.13, 1.04, and 1.02 eV but also a distinct lack of any significant photoluminescence (PL) and a high instability under ambient conditions. These findings enable us to clarify the previously controversial properties of Cs2TiBr6 and establish its role in the vast landscape of perovskite photovoltaics.
CRIS-Team WoS Importer:2022-11-25
Keywords: ball milling; cesium titanium halides; lead-free; stability

Melamine-functionalized graphene oxide: Synthesis, characterization and considering as pseudocapacitor electrode material with intermixed POAP polymer - Ajdari, Farshad Boorboor; Kowsari, Elaheh; Ehsani, Ali; Chepyga, Liudmyla; Schirowski, Milan; Jaeger, Sebastian; Kasian, Olga; Hauke, Frank; Ameri, Tayebeh (Applied Surface Science, 2018)
In this study, Melamine functionalized graphene oxide (FGO-Melamine) was synthesized by chemical route. The prepared functionalized graphene oxide was characterized by different analytical techniques such as FT-IR, Raman spectroscopy, thermogravimetry coupled with mass spectrometry (TG-MS), X-Ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and X-ray photoelectron spectroscopy (XPS). To improve electrochemical properties of polyorthoaminophenol (POAP), the electropolymerized POAP/FGO-Melamine films, employed as an active electrode regarding electrochemical performance. In terms of electrochemical measurements, galvanostatic charge–discharge evaluation, EIS (electrochemical impedance spectroscopy) and CV (cyclic voltammetry) were employed for conducting an enquiry into supercapacitive performance of nanocomposite of POAP/FGO-Melamine. This graphene-based electrode showed a specific capacitance (SC) by 273 F g−1 and high energy of 37.91 W kg−1 at power density of 500 W kg−1. The novel materials synthesized in the current work show higher efficiency compared to the carbon-based ones concerning redox reactions of capacitors consisting of good stability in the existence of aqueous electrolyte, large active surface area and ease synthesis method. © 2018 Elsevier B.
Keywords: Functionalized graphene oxide; Supercapacitor; Characterization; Synthesis

Melting and Crystallization Features of CsPbBr3 Perovskite - Kanak, Andrii; Kopach, Oleg; Kanak, Liliia; Levchuk, Ievgen; Isaiev, Mykola; Brabec, Christoph; Fochuk, Petro; Khalavka, Yuriy (Crystal Growth and Design, 2022)
The all-inorganic perovskite cesium lead bromide (CsPbBr3) has attracted considerable attention as a promising material for optoelectronics and high-energy radiation detectors. In order to obtain a bulk single crystal from a melt, it is crucial to understand the peculiarities of melting and crystallization processes. Here, the solid-liquid and liquid-solid phase transitions were studied by differential thermal analysis at different heating/cooling rates (0.1, 1, 3, 5, and 10 degrees C/min). A two-stage melting mechanism of CsPbBr3 perovskite was proposed. The critical maximal sample temperature (Tcritical) was determined for each heating rate. If the sample was heated to a temperature below Tcritical, the crystallization occurred at a temperature higher than the melting point. Contrarily, if the sample was heated to a temperature higher than this critical value, the melt crystallization occurred with supercooling. We believe that such crystallization features are closely related to the melt structure, which changes during the sample heating. The activation energies of melting and crystallization processes of CsPbBr3 were determined to be 1846 and 1940 kJ/mol, respectively. For the first time, this study demonstrates the impact of heating and cooling conditions on the melting and crystallization processes of the bulk CsPbBr3. It is significant for gaining a fundamental understanding of the crystal growth and fabrication of high-quality monocrystalline materials.
CRIS-Team WoS Importer:2022-07-08

Memory and neural networks on the basis of color centers in solids - Winnacker, Albrecht; Osvet, Andres (Biological Chemistry, 2009)
Optical data recording is one of the most widely used and efficient systems of memory in the non-living world. The application of color centers in this context offers not only systems of high speed in writing and read-out due to a high degree of parallelism in data handling but also a possibility to set up models of neural networks. In this way, systems with a high potential for image processing, pattern recognition and logical operations can be constructed. A limitation to storage density is given by the diffraction limit of optical data recording. It is shown that this limitation can at least in principle be overcome by the principle of spectral hole burning, which results in systems of storage capacities close to the human brain system.
Keywords: Color center; Neural network; Memory; Spectral hole burning; Optical storage; photostimulated luminescence

Methylammonium-free, high-efficiency, and stable all-perovskite tandem solar cells enabled by multifunctional rubidium acetate - Liao, Xufeng; Jia, Xuefei; Li, Weisheng; Lang, Xiting; Zhang, Jianhua; Zhao, Xinyu; Ji, Yitong; Du, Qingguo; Kuan, Chun Hsiao; Ren, Zhiwei; Huang, Wenchao; Bai, Yang; et al. (Nature Communications, 2025)
All-perovskite tandem solar cells (APTSCs) offer the potential to surpass the Shockley-Queisser limit of single-junction solar cells at low cost. However, high-performance APTSCs contain unstable methylammonium (MA) cation in the tin-lead (Sn-Pb) narrow bandgap subcells. Currently, MA-free Sn-Pb perovskite solar cells (PSCs) show lower performance compared with their MA-containing counterparts. This is due to the high trap density associated with Sn2+ oxidation, which is exacerbated by the rapid crystallization of MA-free Sn-containing perovskite. Here, a multifunctional additive rubidium acetate (RbAC) is proposed to passivate Sn-Pb perovskite. We find that RbAC can suppress Sn2+ oxidation, alleviate microstrain, and improve the crystallinity of the MA-free Sn-Pb perovskite. Consequently, the resultant Sn-Pb PSCs achieve a power conversion efficiency (PCE) of 23.02%, with an open circuit voltage (Voc) of 0.897 V, and a filling factor (FF) of 80.64%, and more importantly the stability of the device is significantly improved. When further integrated with a 1.79-electron volt MA-free wide-bandgap PSC, a 29.33% (certified 28.11%) efficient MA-free APTSCs with a high Voc of 2.22 volts is achieved.
CRIS-Team Scopus Importer:2025-02-17

Micron Thick Colloidal Quantum Dot Solids - Fan, James Z.; Vafaie, Maral; Bertens, Koen; Sytnyk, Mykhailo; Pina, Joao M.; Sagar, Laxmi Kishore; Ouellette, Olivier; Proppe, Andrew H.; Rasouli, Armin Sedighian; Gao, Yajun; Baek, Se-Woong; Chen, Bin; et al. (Nano Letters, 2020)
Shortwave infrared colloidal quantum dots (SWIR-CQDs) are semiconductors capable of harvesting across the AM1.5G solar spectrum. Today's SWIR-CQD solar cells rely on spin-coating; however, these films exhibit cracking once thickness exceeds ∼500 nm. We posited that a blade-coating strategy could enable thick QD films. We developed a ligand exchange with an additional resolvation step that enabled the dispersion of SWIR-CQDs. We then engineered a quaternary ink that combined high-viscosity solvents with short QD stabilizing ligands. This ink, blade-coated over a mild heating bed, formed micron-thick SWIR-CQD films. These SWIR-CQD solar cells achieved short-circuit current densities (Jsc) that reach 39 mA cm-2, corresponding to the harvest of 60% of total photons incident under AM1.5G illumination. External quantum efficiency measurements reveal both the first exciton peak and the closest Fabry-Perot resonance peak reaching approximately 80%-this is the highest unbiased EQE reported beyond 1400 nm in a solution-processed semiconductor.
CRIS-Team Scopus Importer:2020-07-31
Keywords: blade coating; infrared photovoltaics; ligand exchange; quantum dots

Micro-optical characterization study of highly p-type doped SiC : Al wafers - Wellmann, Peter; Müller, Ralf; Pons, Michel; Thuaire, A.; Crisci, A.; Mermoux, M.; Auvray, L. (Materials Science Forum, 2005)
We have studied the application of optical techniques for the determination of the spatial distribution of electronic properties of highly aluminum doped p-type SiC wafers. Absorption and birefringence mapping are known to be sensitive characterization methods to determine the homogeneity of charge carrier concentration and defects in n-type SiC. In the case of highly p-type doped SiC these methods fail due to the opaque character of the material. In this paper we show that Raman spectroscopy which is a reflective method can be used in order to address the same materials properties like absorption and birefringence. The study was performed using medium doped p-type SiC:Al where optical transmission and reflection methods can be applied simultaneousl
Keywords: Absorption Mapping; Birefringence; p-Type Doping; Raman Mapping

Micropowder Ca2YMgScSi3O12:Ce Silicate Garnet as an Efficient Light Converter for White LEDs - Shakhno, Anna; Markovskyi, Anton; Zorenko, Tetiana; Witkiewicz-Lukaszek, Sandra; Vlasyuk, Yevheniya; Osvet, Andres; Elia, Jack; Brabec, Christoph; Batentschuk, Miroslaw; Zorenko, Yuriy (Materials, 2022)
This work is dedicated to the crystallization and luminescent properties of a prospective Ca2YMgScSi3O12:Ce (CYMSSG:Ce) micropowder (MP) phosphor converter (pc) for a white light-emitting LED (WLED). The set of MP samples was obtained by conventional solid-phase synthesis using different amounts of B2O3 flux in the 1-5 mole percentage range. The luminescent properties of the CYMSSG:Ce MPs were investigated at different Ce3+ concentrations in the 1-5 atomic percentage range. The formation of several Ce3+ multicenters in the CYMSSG:Ce MPs was detected in the emission and excitation spectra as well as the decay kinetics of the Ce3+ luminescence. The creation of the Ce3+ multicenters in CYMSSG:Ce garnet results from: (i) the substitution by the Ce3+ ions of the heterovalent Ca2+ and Y3+ cations in the dodecahedral position of the garnet host; (ii) the inhomogeneous local environment of the Ce3+ ions when the octahedral positions of the garnet are replaced by heterovalent Mg2+ and Sc3+ cations and the tetrahedral positions are replaced by Si4+ cations. The presence of Ce3+ multicenters significantly enhances the Ce3+ emission band in the red range in comparison with conventional YAG:Ce phosphor. Prototypes of the WLEDs were also created in this work by using CYMSSG:Ce MP films as phosphor converters. Furthermore, the dependence of the photoconversion properties on the layer thickness of the CYMSSG:Ce MP was studied as well. The changes in the MP layer thickness enable the tuning of the white light thons from cold white/daylight to neutral white. The obtained results are encouraging and can be useful for the development of a novel generation of pcs for WLEDs.
CRIS-Team WoS Importer:2022-06-24
Keywords: WLED; phosphor converters; Ca2+-Mg2+-Si4+-based garnets; micropowder; luminescence; Ce3+ multicenters

Micro-powder Ca3Sc2Si3O12:Ce silicate garnets as efficient light converters for WLEDs - Levchuk, Ievgen; Osvet, Andres; Brabec, Christoph; Batentschuk, Miroslaw; Shakhno, Anna; Zorenko, Tetiana; Zorenko, Yuriy (Optical Materials, 2020)
A novel synthesis method of Ca3Sc2Si3O12:Ce micropowder with very bright photo-luminescence (PL) has been developed. The conventional solid-state reaction has been modified for Ca3Sc2Si3O12:Ce microparticle crystallization. Pre-synthesis of metal and silicon oxide blends with subsequent high-temperature treatment in reducing (H2/N2) atmosphere enables obtaining Ca3Sc2Si3O12:Ce micropowder with a high PL quantum yield of about 60–70% at Ce3+ content in the 2.5–5 at.% range, which is highly attractive for LED technology. Additionally, the Ca3Sc2Si3O12:Ce phosphors with Ce concentration in the 0.5–2.5% range display higher thermal stability of photoluminescence in comparison with a commercial YAG:Ce phosphor.
CRIS-Team Scopus Importer:2020-06-02
Keywords: Ca–Si based Garnets; Converters; Luminescence; Micropowder; WLED

Micro-Raman mapping on layers for crystalline silicon thin-film solar cells - Kunz, T.; Hessmann, M. T.; Meidel, B.; Brabec, Christoph (Journal of Crystal Growth, 2011)
Micro-Raman mappings have been used for characterization of our layers system developed for thin-film silicon solar cells. For the cubic SiC barrier layer a preferential orientation of the grains in 〈1 1 1〉 direction normal to the substrate was revealed. A high density of stacking faults resulted in the splitting of transversal optical (TO)-phonon modes, usually only observed in several non-cubic SiC polytypes. Within the silicon layers, which were obtained by zone melting recrystallization (ZMR) and subsequent epitaxial growth, a high residual stress of about 625 MPa was measured near the boundary towards the SiC layer. Outside of this boundary no residual stress could be detected, in spite of commonly found twin boundaries. Thus the main origin of residual stress in the silicon layers is due to the different expansion coefficients of the respective layers, while grain boundaries have no dominant effect. © 2010 Elsevier B.V. All rights reserved.
Keywords: A1. Micro-Raman; A1. Recrystallization; A3. Chemical vapor deposition processes; B2. Semiconducting silicon; B3. Solar cells

Microscopic Deformation Modes and Impact of Network Anisotropy on the Mechanical and Electrical Performance of Five-fold Twinned Silver Nanowire Electrodes - Schrenker, Nadine; Xie, Zhuocheng; Schweizer, Peter; Moninger, Marco; Werner, Felix; Karpstein, Nicolas; Mackovic, Mirza; Spyropoulos, Georgios; Göbelt, Manuela; Christiansen, Silke H.; Brabec, Christoph; Bitzek, Erik; et al. (ACS nano, 2020)
Silver nanowire (AgNW) networks show excellent optical, electrical, and mechanical properties, which make them ideal candidates for transparent electrodes in flexible and stretchable devices. Various coating strategies and testing setups have been developed to further improve their stretchability and to evaluate their performance. Still, a comprehensive microscopic understanding of the relationship between mechanical and electrical failure is missing. In this work, the fundamental deformation modes of five-fold twinned AgNWs in anisotropic networks are studied by large-scale SEM straining tests that are directly correlated with corresponding changes in the resistance. A pronounced effect of the network anisotropy on the electrical performance is observed, which manifests itself in a one order of magnitude lower increase in resistance for networks strained perpendicular to the preferred wire orientation. Using a scale-bridging microscopy approach spanning from NW networks to single NWs to atomic-scale defects, we were able to identify three fundamental deformation modes of NWs, which together can explain this behavior: (i) correlated tensile fracture of NWs, (ii) kink formation due to compression of NWs in transverse direction, and (iii) NW bending caused by the interaction of NWs in the strained network. A key observation is the extreme deformability of AgNWs in compression. Considering HRTEM and MD simulations, this behavior can be attributed to specific defect processes in the five-fold twinned NW structure leading to the formation of NW kinks with grain boundaries combined with V-shaped surface reconstructions, both counteracting NW fracture. The detailed insights from this microscopic study can further improve fabrication and design strategies for transparent NW network electrodes.<br
Keywords: silver nanowire; five-fold twinning; transparent electrode; buckling; kinks; transmission electron microscopy; molecular dynamics

Microsecond carrier lifetimes in bulk-like 3C-SiC grown by sublimation epitaxy - Sun, Jianwu; Kamiyama, Satoshi; Wellmann, Peter; Liljedahl, Rickard; Yakimova, Rositsa; Syväjärvi, Mikael (Materials Science Forum, 2013)
High quality bulk-like 3C-SiC were grown on on-axis (0001) 6H-SiC substrate by sublimation epitaxy. The microwave photoconductivity decay mapping measurements revealed that this material shows considerable long carrier lifetimes varied from 3.519 to 7.834 mu s under the injection level of 3.5x10(12) cm(-2), which are comparable with the best carrier lifetimes in 4H-SiC layers. The mapping of high resolution x-ray diffraction obtained from the same region shows that smaller carrier lifetimes seem to correspond to the larger FWHM values and vice versa. This shows that long carrier lifetime obtained in 3C-SiC is due to the improvement of the crystal qualit
Keywords: 3C-SiC; carrier lifetime; HR-XRD

Microstructure instabilities in solution-processed organic bulk-heterojunction solar cells - Li, Ning; Zhang, Chaohong; Brabec, Christoph (7th IEEE World Conference on Photovoltaic Energy Conversion, WCPEC 2018, 2018)
The performance of organic solar cells (OSCs) is determined by the delicate, meticulously optimized bulkheterojunction microstructure, which consists of finely mixed and relatively separated donor/acceptor regions. In this work we examine the reliability and stability of bulk-heterojunction (BHJ) microstructures of a highly-efficiency OSC based on PCE11 as the donor and PCBM as the acceptor. The so called burn-in degradation is identified as a spinodal de-mixing due to the low miscibility of donor and acceptor, which is turned out to be a major challenge for the development of stable and efficient OSCs. Even though the microstructure can be kinetically tuned for achieving high-performance, the inherently low miscibility of donor and acceptor leads to spontaneous phase separation in the solid state, even at room temperature and in the dark. The construction of the spinodal phase diagrams highlight molecular incompatibilities between the donor and acceptor as a dominant mechanism for burn-in degradation, which is to date the major short-time loss reducing the performance and stability of organic solar cells<br
Keywords: donor-acceptor demixing; bulk-heterojunction; miscibility; microstructure stability; organic photovoltaic cells

Mitigation of carrier trapping effects on carrier lifetime measurements with continuous-wave laser illumination for Pb-based metal halide perovskite materials - Lobo, Ntumba; Matt, Gebhard; Osvet, Andres; Shrestha, Shreetu; Kanak, Andrii; Fochuk, Petro; Brabec, Christoph; Kato, Masashi (Journal of Applied Physics, 2024)
We investigated the impact of carrier trapping on the carrier lifetime of metal halide perovskite materials, which are key to solar cell production. We examined NH3CH3PbI3 (MAPbI3), NH3CH3PbBr3 (MAPbBr3), and CsPbBr3 using continuous-wave (CW) laser illumination during microwave photoconductivity decay (μ-PCD) measurements. Traditional pulsed light excitation falls short of mirroring solar cell operating conditions, owing to carrier trapping. Implementing CW laser illumination provides a more accurate estimation of the carrier lifetimes under operational conditions. With an increased photon flux from the CW laser, the μ-PCD decay curves changed, indicating reduced recombination via traps. The experiments revealed extended carrier lifetimes under continuous light for the MAPbI3 polycrystal. This suggests that CW lasers can mitigate trapping effects on carrier lifetime measurements. For the other samples, carrier trapping had a negligible effect on the measured carrier lifetimes. We believe that these findings will aid in the design of perovskite-based devices.
CRIS-Team Scopus Importer:2024-05-03

Mixed 2D-Dion-Jacobson/3D Sn-Pb alloyed perovskites for efficient photovoltaic solar devices - Lu, Zhili; Li, Chaohui; Lai, Hongwei; Zhou, Xinming; Wang, Chunfeng; Liu, Xianhu; Guo, Fei; Pan, Caofeng (Nano Research, 2022)
Tin-lead (Sn-Pb) alloyed perovskites with tunable bandgaps hold great potential for constructing highly efficient single-junction and tandem photovoltaic devices. However, the efficiency and stability of Sn-Pb perovskite solar cells (PSCs) are greatly hampered by severe nonradiative recombination due to the easy oxidation of Sn(II). In this work, we report the construction of mixed dimensional two-dimensional (2D) Dion-Jacobson (DJ) and three-dimensional (3D) perovskites to improve the efficiency and stability of Sn-Pb alloyed PSCs. Introducing a small amount of 1,4-butanediammonium diiodide as spacer cations of DJ perovskites into precursor, the prepared mixed dimensional Sn-Pb alloyed perovskites exhibit reduced trap-state density due to the passivation of 2D DJ perovskites. As a result, nonradiative charge recombination is greatly suppressed. The prepared Sn-Pb alloyed PSCs based on 2D-DJ/3D heterojunction deliver a power conversion efficiency of 19.02% with an impressive fill factor of 80%. As well, improved device stability is realized due to the presence of DJ perovskites which serves as a protection barrier against oxidation and water invasion.
CRIS-Team WoS Importer:2022-10-14

Modeling and experimental verification of SiC M-PVT bulk crystal growth - Wellmann, Peter; Müller, Ralf; Pons, Michel (Materials Science Forum, 2006)
We have studied the impact of the chemical nature of additional gases fed into the modified physical vapor transport (M-PVT) growth cell. In particular experiments were carried out using helium, argon, nitrogen and propane in the growth setup. Numerical modeling was used to address the underlying physical and chemical effects that impact the global temperature field. It is found that chemical decomposition of complex gases plays a secondary role as heat source or sink. However, temperature variations related to varying gas compositions fed to the systems are primarily induced by changes of the graphite foam isolation propertie
Keywords: Modeling; M-PVT; Sublimation Growth

Modeling of the mass transport during the homo-epitaxial growth of silicon carbide by fast sublimation epitaxy - Hupfer, Thomas; Hens, Philip; Kaiser, Michl; Jokubavicius, Valdas; Syväjärvi, Mikael; Wellmann, Peter (Materials Science Forum, 2013)
Two growth regions with different limitation of growth speed are observed in the fast sublimation growth process of silicon carbide. Using suggested theoretical model for the mean free path calculations, the influences of temperature and inert gas pressure on the mass transport for the growth of epitaxial layers were considered theoretically and confirmed by experimental data. © (2013) Trans Tech Publications, Switzerlan
Keywords: Mass Transport; Modeling; Silicon Carbide (SiC); Sublimation Epitaxy

Modeling of the PVT Growth Process of Bulk 3C-SiC - Growth Process Development and Challenge of the Right Materials Data Base - Schöler, Michael; Schuh, Philipp; Steiner, Johannes; Wellmann, Peter (Materials Science Forum, 2019)
We report on the modeling of the temperature field and supersaturation in front of the SiC crystal growth interface of a physical vapor transport growth configuration. The data are compared with experimental results, like the growth of free standing 3C-SiC wafers with a diameter of 50 mm and a thickness of 870 µm. Special emphases is put on the precise handling of the materials properties which include the temperature dependency of the heat and electrical conductivity of the graphite parts at temperatures above 2000 °C.
Keywords: 3C Polytype; Numerical Modelling; Silicon Carbide; Vapor Growth

Modified physical vapor transport growth of SiC - Control of gas phase composition for improved process conditions - Wellmann, Peter; Straubinger, Thomas; Desperrier, Patrick; Müller, Ralf; Künecke, Ulrike; Sakwe, Aloysius; Schmitt, H.; Winnacker, Albrecht; Blanquet, E.; Dedulle, J.M.; Pons, Michel (Materials Science Forum, 2005)
We review the development of a modified physical vapor transport (M-PVT) growth technique for the preparation of SiC single crystals which makes use of an additional gas pipe into the growth cell. While the gas phase composition is basically fixed in conventional physical vapor transport (PVT) growth by crucible design and temperature field, the gas inlet of the M-PVT configuration allows the direct tuning of the gas phase composition for improved growth conditions. The phrase "additional" means that only small amounts of extra gases are supplied in order to fine-tune the gas phase composition. We discuss the experimental implementation of the extra gas pipe and present numerical simulations of temperature field and mass transport in the new growth configuration. The potential of the growth technique will be outlined by showing the improvements achieved for p-type doping of 4H-SiC with aluminum, i.e. [Al]=9-10(19)cm(-3) and p< 0.2&UOmega; cm, and n-type doping of SiC with phosphorous, i.e. [P]=7.8(.)10(17)cm(-3
Keywords: Doping; M-PVT Growth; Numerical Modeling

Modified Synthesis of Cs4PbBr6 for Enhanced Purity and Quantum Yield and for Exploring Its Potential as a High Stokes Shift Material for Down-Conversion in Solar Cells - Darwish, Elshaimaa; Elia, Jack; Barabash, Anastasia; Hu, Huiying; Batentschuk, Miroslaw; Osvet, Andres (Advanced Engineering Materials, 2024)
Energy demands have kept increasing in recent years due to expanding human activity. Silicon solar cells offer an attractive renewable energy source while their external quantum efficiency (EQE) can still be enhanced; one way of doing this is by applying a photon energy downshifting layer. Herein, Cs4PbBr6 is applied as a downshifting layer; the Cs4PbBr6 is synthesized in the form of colloidal nanoparticles, and several modifications are introduced to the synthesis process, resulting in the enhancement of the photoluminescence quantum yield, improving the particle size distribution and reducing the CsBr impurities which appear as a side product during the synthesis of Cs4PbBr6. The application of the produced modified particles in the form of thin films on the top of Si solar cells shows an enhancement of the (EQE) of the solar cells when compared to the unmodified particles.
CRIS-Team Scopus Importer:2024-06-07
Keywords: 0D Cesium lead halide; down conversion; enhancing quantum yield; perovskite nanoparticles; silicon solar cells

Modulating Trapping in Low-Dimensional Lead–Tin Halides for Energy-Efficient Neuromorphic Electronics - Chen, Lijun; Saleh, Saad; Tavormina, Filippo; Di Mario, Lorenzo; Li, Jiaxiong; Xie, Zhiqiang; Masciocchi, Norberto; Brabec, Christoph J.; Koldehofe, Boris; Loi, Maria Antonietta (Advanced Materials, 2025)
Metal halide perovskites have drawn great attention for neuromorphic electronic devices in recent years, however, the toxicity of lead as well as the variability and energy consumption of operational devices still pose great challenges for further consideration of this material in neuromorphic computing applications. Here, a 2D Ruddlesden-Popper (RP) metal halides system of formulation BA2Pb0.5Sn0.5I4 (BA = n-butylammonium) is prepared that exhibits outstanding resistive switching memory performance after cesium carbonate (Cs2CO3) deposition. In particular, the device exhibits excellent switching characteristics (endurance of 5 × 105 cycles, ON/OFF ratio ≈105) and achieves 90.1% accuracy on the MNIST dataset. More importantly, a novel energy-efficient content addressable memory (CAM) architecture building on perovskite memristive devices for neuromorphic applications, called nCAM, is proposed, which has a minimum energy consumption of ≈0.025 fJ bit/cell. A mechanism involving the manipulation of trapping states through Cs2CO3 deposition is proposed to explain the resistive switching behavior of the memristive device.
CRIS-Team Scopus Importer:2025-04-11
Keywords: 2D layered Pb─Sn perovskite; analog CAM; neuromorphic computing; trap states

Module-Power Prediction from PL Measurements using Deep Learning - Hoffmann, Mathis; Hepp, Johannes; Doll, Bernd; Buerhop-Lutz, Claudia; Peters, Ian Marius; Brabec, Christoph; Maier, Andreas; Christlein, Vincent (IEEE Photovoltaic Specialists Conference, 2021)
The individual causes for power loss of photovoltaic modules are investigated for quite some time. Recently, it has been shown that the power loss of a module is, for example, related to the fraction of inactive areas. While these areas can be easily identified from electroluminescense (EL) images, this is much harder for photoluminescence (PL) images. With this work, we close the gap between power regression from EL and PL images. We apply a deep convolutional neural network to predict the module power from PL images with a mean absolute error (MAE) of 4.4% or 11.7WP. Furthermore, we depict that regression maps computed from the embeddings of the trained network can be used to compute the localized power loss. Finally, we show that these regression maps can be used to identify inactive regions in PL images as wel
Keywords: photoluminescence; power; regression; deep learning; weakly supervised

Molecular Design of Hole Transport Materials to Immobilize Ion Motion for Photostable Perovskite Solar Cells - Zhang, Zheng; Duan, Chenghao; Wang, Sijing; Xie, Tianyou; Zou, Feilin; Luo, Yang; Tang, Ruijia; Guo, Kunpeng; Yuan, Ligang; Zhang, Kaicheng; Wang, Yao; Qiu, Jianhang; et al. (Angewandte Chemie International Edition, 2024)
Poor operational stability is a crucial factor limiting the further application of perovskite solar cells (PSCs). Organic semiconductor layers can be a powerful means for reinforcing interfaces and inhibiting ion migration. Herein, two hole-transporting molecules, pDPA-SFX and mDPA-SFX, are synthesized with tuned substituent connection sites. The meta-substituted mDPA-SFX results in a larger dipole moment, more ordered packing, and better charge mobility than pDPA-SFX, accompanying with strong interface bonding on perovskite surfaces and suppressed ion motion as well. Importantly, mDPA-SFX-based PSCs exhibit an efficiency that has significantly increased from 22.5 % to 24.8 % and a module-based efficiency of 19.26 % with an active area of 12.95 cm2. The corresponding cell retain 94.8 % of its initial efficiency at maximum power point tracking (MPPT) after 1,000 h (T95=1,000 h). The MPPT T80 lifetime is as long as 2,238 h. This work illustrates that a small degree of structural variation in organic compounds leaves considerable room for developing new HTMs for light stable PSCs.
CRIS-Team Scopus Importer:2024-10-25
Keywords: hole-transporting molecule; interface bonding; ion migration; perovskite solar cells; photostability

Molecular Donor–Acceptor Dyads for Efficient Single-Material Organic Solar Cells - Lucas, Sebastian; Kammerer, Jochen; Pfannmoeller, Martin; Schroeder, Rasmus R.; He, Yakun; Li, Ning; Brabec, Christoph; Leydecker, Tim; Samori, Paolo; Marszalek, Tomasz; Pisula, Wojchiech; Mena-Osteritz, Elena; et al. (Solar RRL, 2020)
Single-material organic solar cells (SMOSCs) promise several advantages with respect to prospective applications in printed large-area solar foils. Only one photoactive material has to be processed and the impressive thermal and photochemical long-term stability of the devices is achieved. Herein, a novel structural design of oligomeric donor–acceptor (D–A) dyads 1–3 is established, in which an oligothiophene donor and fullerene acceptor are covalently linked by a flexible spacer of variable length. Favorable optoelectronic, charge transport, and self-organization properties of the D–A dyads are the basis for reaching power conversion efficiencies up to 4.26% in SMOSCs. The dependence of photovoltaic and charge transport parameters in these ambipolar semiconductors on the specific molecular structure is investigated before and after post-treatment by solvent vapor annealing. The inner nanomorphology of the photoactive films of the dyads is analyzed with transmission electron microscopy (TEM) and grazing-incidence wide-angle X-ray scattering (GIWAXS). Combined theoretical calculations result in a lamellar supramolecular order of the dyads with a D–A phase separation smaller than 2 nm. The molecular design and the precise distance between donor and acceptor moieties ensure the fundamental physical processes operative in organic solar cells and provide stabilization of D–A interfaces.
CRIS-Team Scopus Importer:2020-12-04
Keywords: ambipolar charge transport; donor–acceptor dyads; fullerenes; oligothiophenes; single-material organic solar cells

Molecular Doping of a Hole-Transporting Material for Efficient and Stable Perovskite Solar Cells - Luo, Junsheng; Zhu, Jinqing; Lin, Fangyan; Xia, Jianxing; Yang, Hua; JinyuYang, None; Wang, Ruilin; Yuan, Junyu; Wan, Zhongquan; Li, Ning; Brabec, Christoph; Jia, Chunyang (Chemistry of Materials, 2022)
The bis(trifluoromethane)sulfonimide lithium salt (Li-TFSI) is commonly used as an effective dopant to improve the conductivity and hole mobility of Spiro-OMeTAD in state-of-the-art n-i-p perovskite solar cells (PSCs). However, such doping severely induces device instability because of the ultrahygroscopic and migratory nature of Li+ ions. Here, we demonstrate a fluorinated Fe(F20TPP)Cl with a hydrophobic property and a high migration barrier as a potential alternative to replace the Li-TFSI in doped Spiro-OMeTAD. The optimized PSCs show a champion power conversion efficiency as high as 21.53% with a stabilized efficiency exceeding 21%. In addition, long-term stability of PSCs is significantly improved, and the device retains 84% of its initial efficiency after 900 h under continuous 100 mW cm-2 white light-emitting diode illumination and 89% of its initial efficiency after even 50 days in an ambient environment without encapsulation. We believe that this work addresses the fundamental question of intrinsic and extrinsic instability in Li-TFSI-based PSCs by combining simulation and experimental studies. The novel dopant Fe(F20TPP)Cl developed for Spiro-OMeTAD in this work can effectively meet the demands of future photovoltaic applications with promising efficiency and device stability.
CRIS-Team Scopus Importer:2022-04-01

Molecular-Level Hybridization of Nafion with Quantum Dots for Highly Enhanced Proton Conduction - Wu, Wenjia; Li, Yifan; Liu, Jindun; Wang, Jingtao; He, Yakun; Davey, Kenneth; Qiao, Shi-Zhang (Advanced Materials, 2018)
Nanophase-separated membranes hold promise for fast molecule or ion transfer. However, development and practical application are significantly hindered by both the difficulty of chemical modification and nanophase instability. This can be addressed by organic–inorganic hybridization of functional fillers with a precise distribution in specific nanophase. Here, a molecular-level hybridization for nanophase-separated Nafion using 2–5 nm quantum dots (QDs) as a new smart filler is demonstrated. Two kinds of QDs are prepared and used: hydrophilic polymer-like QDs (PQDs) and hydrophobic graphene oxide QDs (GQDs). Because of selective interactions, QDs offer advantages of matched structural size and automatic recognition with the nanophase. A distinctive synthesis of subordinate-assembly, in which QDs are driven by the self-assembly of Nafion affinity chains, is reported. This results in a precise distribution of QDs in the ionic, or backbone, nanophases of Nafion. The resulting PQDs in the ionic nanophase significantly increase membrane proton conduction and device output-power without loss of mechanical stability. This is difficult to realize with conventional fillers. The GQDs in the backbone nanophase reduce the crystallinity and significantly augment membrane water uptake and swelling capacities. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhe
Keywords: molecule-level hybridization; nanophase-separated membrane; hydrogen fuel cell; proton conduction; quantum dots

Molecular Oligothiophene–Fullerene Dyad Reaching Over 5% Efficiency in Single-Material Organic Solar Cells - Aubele, Anna; He, Yakun; Kraus, Teresa; Li, Ning; Mena-Osteritz, Elena; Weitz, Paul; Heumüller, Thomas; Zhang, Kaicheng; Brabec, Christoph; Bäuerle, Peter (Advanced Materials, 2021)
A novel donor–acceptor dyad, 4, in which the conjugated oligothiophene donor is covalently connected to fullerene PC71BM by a flexible alkyl ester linker, is synthesized and applied as photoactive layer in solution-processed single-material organic solar cells (SMOSCs). Excellent photovoltaic performance, including a high short-circuit current density (JSC) of 13.56 mA cm−2, is achieved, leading to a power conversion efficiency of 5.34% in an inverted cell architecture, which is substantially increased compared to other molecular single materials. Furthermore, dyad 4-based SMOSCs display excellent stability maintaining 96% of the initial performance after 750 h (one month) of continuous illumination and operation under simulated AM 1.5G irradiation. These results will strengthen the rational molecular design to further develop SMOSCs for potential industrial application.
CRIS-Team Scopus Importer:2021-09-10
Keywords: charge transport; device performance; donor–acceptor dyads; long-term stability; single-material organic solar cells

Monitoring and assessment of PV generation based on a combination of smart metering and thermographic measurement - Stegner, C.; Dalsass, M.; Luchscheider, P.; Brabec, Christoph (Solar Energy, 2018)
Electrical solar power generation has a very decentral character which is posing significant challenges to monitoring and assessment due to the high number of considered systems. At the same time, with the advent of smart metering, huge amounts of data are becoming available and demand for automated approaches that are robust enough to deal with measuring gaps and noise. We propose and introduce a combined method consisting of a fitting algorithm, which works with the high temporal resolution of the smart meter data used (15 s), and an infrared thermography measurement. The results are region-specific irradiance characteristics, precise description of individual skylines for single systems derived from calculations, indication of abnormalities that should be compared with the abnormalities identified in thermal images and identification of reasons for underperformance.
Keywords: Aerial infrared thermography; Module defects; PV simulation; Smart metering

Morphological and electrical control of fullerene dimerization determines organic photovoltaic stability - Heumüller, Thomas; Mateker, William R.; Distler, Andreas; Fritze, Urs F.; Cheacharoen, Rongrong; Nguyen, William H.; Biele, Markus; Salvador, Michael Filipe; von Delius, Max; Egelhaaf, Hans-Joachim; Mcgehee, Michael D.; Brabec, Christoph (Energy and Environmental Science, 2016)
Fullerene dimerization has been linked to short circuit current (J) losses in organic solar cells comprised of certain polymer-fullerene systems. We investigate several polymer-fullerene systems, which present J loss to varying degrees, in order to determine under which conditions dimerization occurs. By reintroducing dimers into fresh devices, we confirm that the photo-induced dimers are indeed the origin of the J loss. We find that both film morphology and electrical bias affect the photodimerization process and thus the associated loss of J. In plain fullerene films, a higher degree of crystallinity can inhibit the dimerization reaction, as observed by high performance liquid chromatography (HPLC) measurements. In blend films, the amount of dimerization depends on the degree of mixing between polymer and fullerene. For highly mixed systems with very amorphous polymers, no dimerization is observed. In solar cells with pure polymer and fullerene domains, we tune the fullerene morphology from amorphous to crystalline by thermal annealing. Similar to neat fullerene films, we observe improved light stability for devices with crystalline fullerene domains. Changing the operating conditions of the investigated solar cells from V to J also significantly reduces the amount of dimerization-related J loss; HPLC analysis of the active layer shows that more dimers are formed if the cell is held at V instead of J. The effect of bias on dimerization, as well as a clear correlation between PL quenching and reduced dimerization upon addition of small amounts of an amorphous polymer into PC60BM films, suggests a reaction mechanism via excitons.
Keywords: Engineering controlled terms: Amorphous films; Crystalline materials; Dimerization; Dimers; Fullerenes; High performance liquid chromatography; Liquid chromatography; Organic polymers; Polymer films; Polymers Amorphous polymers; Crystalline fullerene; Degree of crystallinity; Dimerization reactions; Electrical control; Operating condition; Organic photovoltaics; Polymer-fullerene system Engineering main heading: Solar cells

Morphological and optical stability in growth of fluorescent SiC on low off-axis substrates - Jokubavicius, Valdas; Kaiser, Michl; Hens, Philip; Wellmann, Peter; Liljedahl, Rickard; Yakimova, Rositsa; Syväjärvi, Mikael (Materials Science Forum, 2013)
Fluorescent silicon carbide was grown using the fast sublimation growth process on low off-axis 6H-SiC substrates. In this case, the morphology of the epilayer and the incorporation of dopants are influenced by the Si/C ratio. Differently converted tantalum foils were introduced into the growth cell in order to change vapor phase stochiometry during the growth. Fluorescent SiC grown using fresh and fully converted tantalum foils contained morphological instabilities leading to lower room temperature photoluminescence intensity while an improved morphology and optical stability was achieved with partly converted tantalum foil. This work reflects the importance of considering the use of Ta foil in sublimation epitaxy regarding the morphological and optical stability in fluorescent silicon carbid
Keywords: fluorescent SiC; low off-axis substrates; sublimation epitaxy

Morphological impact of zinc oxide layers on the device performance in thin-film transistors - Faber, Hendrik; Klaumünzer, Martin; Voigt, Michael; Galli, Diana; Vieweg, Benito; Peukert, Wolfgang; Spiecker, Erdmann; Halik, Marcus (Nanoscale, 2011)
Zinc oxide thin-films are prepared either by spin coating of an ethanolic dispersion of nanoparticles (NP, diameter 5 nm) or by spray pyrolysis of a zinc acetate dihydrate precursor. High-resolution electron microscopy studies reveal a monolayer of particles for the low temperature spin coating approach and larger crystalline domains of more than 30 nm for the spray pyrolysis technique. Thin-film transistor devices (TFTs) based on spray pyrolysis films exhibit higher electron mobilities of up to 24 cm² V−1 s−1 compared to 0.6 cm² V−1 s−1 for NP based TFTs. These observations were dedicated to a reduced number of grain boundaries within the transistor channel.

Morphology analysis of near IR sensitized polymer/fullerene organic solar cells by implementing low bandgap heteroanalogue C-/Si-PCPDTBT - Ameri, Tayebeh; Khoram, Parisa; Heumüller, Thomas; Baran, Derya; Machui, Florian; Troeger, Anna; Sgobba, Vito; Guldi, Dirk Michael; Halik, Marcus; Rathgeber, Silke; Scherf, Ullrich; Brabec, Christoph (Journal of Materials Chemistry A, 2014)
In the current work, we have investigated the morphological aspects of the ternary solar cells based on host matrices of P3HT:PCBM and P3HT:ICBA, using the low bandgap polymer analogues of C- and Si-bridged PCPDTBT as near IR sensitizers, which show noticeably different performance. A direct comparison of these well-functional and poorly functional ternary blend systems provides insights into the bottlenecks of device performance and enables us to set up an initial set of design rules for ternary organic solar cells. Our study reveals the importance of surface energy as a driving force controlling sensitizer location and morphology formation of ternary blends. The interfacial surface energy results indicate that Si-PCPDTBT locates at amorphous interfaces and P3HT crystallites, while C-PCPDTBT tends to accumulate at amorphous interfaces and semi-crystalline (or agglomerated) domains of the fullerene derivatives. GIWAXS and SCLC results support this prediction where adding high content of C-PCPDTBT influences mainly the semi-crystallinity (aggregation) of the fullerene and reduces the electron mobility, but Si-PCPDTBT impacts mainly the P3HT ordering and, in turn, deteriorates the hole mobility. These findings show that the disruption of the fullerene semi-crystalline domains is more detrimental to the device performance than the disruption of the polymer domains.

Morphology-Controlled Organic Solar Cells Improved by a Nanohybrid System of Single Wall Carbon Nanotubes Sensitized by PbS Core/Perovskite Epitaxial Ligand Shell Quantum Dots - Soltani, Rezvan; Katbab, Ali Asghar; Sytnyk, Mykhailo; Amin, Atefeh Y.; Killilea, Niall Andrew; Berlinghof, Marvin; Ahmadloo, Farzaneh; Osvet, Andres; Unruh, Tobias; Heiß, Wolfgang; Ameri, Tayebeh (Solar RRL, 2017)
In the present work, a new solution processed nanohybrid system comprising of single-wall carbon nanotubes (SWCNTs) loaded by PbS quantum dots (QD) capped with an epitaxial ligand shell of methylammonium lead iodide perovskite clusters (MA4PbI6) is designed and fabricated. Attachment of PbS/PbI6 QDs on the surface of SWCNT is followed and evidenced by performing Fourier Transform Infrared Spectroscopy, X-ray photoelectron spectroscopy, and Field Emission Scanning Electron Microscopy. The steady state and dynamic photoluminescence results reveal efficient charge transfer from photo-excited PbS/PbI6 to SWCNTs. Very low amount (0.3 wt.%) of the as-synthesized PbS/PbI6-SWCNT is further incorporated into a polymeric solar cell containing P3HT and PC61BM and exhibits a power conversion efficiency improvement of around 15% compared to the P3HT:PC61BM bulk heterojunction reference solar cell. Significantly, loading perovskite capped PbS QDs on the surface of SWCNT works more efficient rather than incorporating PbS/PbI6 or SWCNT separately onto the composition of the photoactive layer. While PbS/PbI6 broaden the absorption window of photoactive layer and enhance the photon harvesting, their loading on the SWCNT has a significant influence on the faster exciton splitting by efficient electron transfer as well as keeping the desired crystallinity and nanoscale morphology of host matrix upon addition of QDs.

Morphology optimization via molecular weight tuning of donor polymer enables all-polymer solar cells with simultaneously improved performance and stability - Li, Zhenye; Zhong, Wenkai; Ying, Lei; Liu, Feng; Li, Ning; Huang, Fei; Cao, Yong (Nano Energy, 2019)
Organic solar cells with excellent device performance and stability are essential for both academic and industrial purposes. The molecular weight (Mn) of donor polymers plays a critical role in determining the photovoltaic properties of all-polymer solar cells (all-PSCs). Despite Mn of donor polymers has pronounced effects on microstructure morphology, photovoltaic performance and stability of all-PSCs are rarely analyzed and understood in high-performance devices. In this study, we systematically investigate the influence of Mn of donor polymers on the device performance metrics and device stability of all-PSCs comprising of a wide-bandgap polymer donor PTzBI-Si and a polymer acceptor N2200. All-PSCs based on high Mn of PTzBI-Si exhibit an excellent PCE of 11.5% with improved stability, which is clearly superior to that of all-PSCs based on low Mn of PTzBI-Si. The photovoltaic performance difference caused by Mn of PTzBI-Si is systematically characterized and analysed to establish the morphology-property-performance correlation. The findings demonstrated in our model system suggest that tuning the Mn of donor polymer could be a facile and promising strategy to simultaneously enhance the efficiency and stability of all-PSCs.
CRIS-Team Scopus Importer:2019-08-13
Keywords: All-polymer solar cell; Molecular weight; Morphology optimization; Stability

Morphology Optimization via Side Chain Engineering Enables All Polymer Solar Cells with Excellent Fill Factor and Stability - Liu, Xi; Zhang, Chaohong; Duan, Chunhui; Li, Mengmeng; Hu, Zhicheng; Wang, Jing; Liu, Feng; Li, Ning; Brabec, Christoph; Janssen, Rene A. J.; Bazan, Guillermo C.; Huang, Fei; et al. (Journal of the American Chemical Society, 2018)
All-polymer solar cells (all-PSCs) composed of conjugated polymers as both donor and acceptor components in bulk heterojunction photoactive layers have attracted increasing attention. However, it is a big challenge to achieve optimal morphology in polymer:polymer blends. In response, we report herein a new strategy to adjust the nanoscale organization for all-PSCs. Specifically, side chain engineering of the well-known naphthalene diimide (NDI)-based polymer N2200 is modulated by introducing a fraction of linear oligoethylene oxide (OE) side chains to replace branched alkyl chains on the NDI units and by synthesizing a series of NDI-based polymer acceptors NOEx, where x is the percentage of OE chain substituted NDI units relative to total NDI units. Compared to the reference polymer NOE0, OE-chain-containing polymer NOE10 offers a much higher power conversion efficiency (PCE) of 8.1% with a record high fill factor (FF) of 0.75 in all-PSCs. Moreover, the NOE10-based all-PSC exhibits excellent long-term and thermal stabilities with >97% of the initial PCE being maintained after 300 h of aging at 65 degrees C. This work demonstrates an effective morphology optimization strategy to achieve highly efficient and stable all-PSCs and shows the excellent potential of NOE10 as an alternative to commercially available acceptor polymers N2200.
Keywords: Cell engineering; Conjugated polymers; Heterojunctions; Morphology; Naphthalene; Nondestructive examination; Polymer blends; Solar cells

Morphology related photodegradation of low-band-gap polymer blends - Wang, Xiao; Egelhaaf, Hans-Joachim; Mack, Hans-Georg; Azimi, Seyed Hamed; Brabec, Christoph; Meixner, Alfred J.; Zhang, Dai (Advanced Energy Materials, 2014)
The morphology related photodegradation of low band-gap polymer blends is investigated using optical microscopy and scanning probe microscopy. Poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (C-PCPDTBT):[6,6]-phenyl C61-butyric acid methyl ester (PCBM) blend films without and with ODT, as well as poly[(4,40-bis(2-ethylhexyl)dithieno[3,2-b:20,30-d]silole)-2,6-diylalt-(2,1,3-benzothiadiazole)-4,7-diyl] (Si-PCPDTBT):PCBM blend films exposed to a focused 632.8 nm laser under ambient condition with and without inert gas protection are studied. The photodegradation of the polymer starts in the vicinity of the PCBM molecules (first sphere degradation), which effectively blocks the electron transfer processes. Stern-Volmer type kinetics are observed in the C-PCPDTBT:PCBM blend with ODT, which indicates that only a small number of photo-oxidized monomer units act as quenchers of the C-PCPDTBT polymer luminescence. Furthermore, in addition to the permanent damage of the polymer molecules, as witnessed from their Raman intensity decrease, the polymer photoluminescence demonstrates partial reversible recovery when inert gas protection is resumed, indicating the involvement of temporary polymer/O-charge transfer complexes in the photodegradation process.
Keywords: Nanoscale morphology; Phase separation; Photodegradation; Polymer blend films

Multifunctional Reductive Molecular Modulator toward Efficient and Stable Perovskite Solar Cells - Li, Mengjia; Gao, Deyu; Zhang, Boxue; Xu, Sai; Zhuang, Xinmeng; Wang, Chen; Yang, Liqun; Ma, Xiaohui; Zheng, Shijian; Song, Hongwei; Chen, Jiangzhao; Chen, Cong (Solar RRL, 2021)
The defects (e.g., I2, anion, and cation vacancies) in the perovskite films are detrimental to the power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). Herein, a multifunctional additive molecule 4-fluorophenylhydrazine hydrochloride (denoted as 4F-PHCl) is reported, which can improve perovskite crystallization, passivate film defects, and enhance film moisture stability, finally leading to the simultaneous increase in PCE and stability. It is revealed that the hydrazine functional group can effectively reduce the I2 defects back to I-. In addition, the hydrazinium contained cations and chloride anions can passivate the cationic defects (like anion vacancies) and anionic defects (like cation vacancies), respectively. The hydrophobic fluorinated benzene ring should be mainly responsible for the enhanced moisture stability of films and devices. As a result, the 4F-PHCl-modified device achieves a promising efficiency of 21.80% along with a high open-circuit voltage of 1172 mV and exhibits excellent long-term ambient stability. A guide for developing multifunctional additive molecules for the simultaneous enhancement of efficiency and stability is provided.
CRIS-Team Scopus Importer:2021-08-27
Keywords: crystallization modulation; defect passivation; hydrazine; multifunctional additives; reductive additives

Multiscale Simulations for Defect-Controlled Processing of Group IV Materials - Calogero, Gaetano; Deretzis, Ioannis; Fisicaro, Giuseppe; Kollmuß, Manuel; La Via, Francesco; Lombardo, Salvatore F.; Schöler, Michael; Wellmann, Peter; La Magna, Antonino (Crystals, 2022)
Multiscale approaches for the simulation of materials processing are becoming essential to the industrialization of future nanotechnologies, as they allow for a reduction in production costs and an enhancement of devices and applications. Their integration as modules of "digital twins", i.e., a combined sequence of predictive chemical-physical simulations and trained black-box techniques, should ideally complement the real sequence of processes throughout all development and production stages, starting from the growth of materials, their functional manipulation and finally their integration in nano-devices. To achieve this framework, computational implementations at different space and time scales are necessary, ranging from the atomistic to the macro-scale. In this paper, we propose a general paradigm for the industrially driven computational modeling of materials by deploying a multiscale methodology based on physical-chemical simulations bridging macro, meso and atomic scale. We demonstrate its general applicability by studying two completely different processing examples, i.e., the growth of group IV crystals through physical vapor deposition and their thermal treatment through pulsed laser annealing. We indicate the suitable formalisms, as well as the advantages and critical issues associated with each scale, and show how numerical methods for the solution of the models could be coupled to achieve a complete and effective virtualization of the process. By connecting the process parameters to atomic scale modifications such as lattice defects or faceting, we highlight how a digital twin module can gain intrinsic predictivity far from the pre-assessed training conditions of black-box "Virtual Metrology" techniques.
CRIS-Team WoS Importer:2023-01-20

Nanocrystal V2O5 thin film as hole-extraction layer in normal architecture organic solar cells - Wang, Hao; Li, Ning; Güldal, Nusret Sena; Brabec, Christoph (Organic Electronics, 2012)
Nanocrystal VO dispersion processed thin films are introduced as efficient hole extraction interlayer in normal architecture P3HT:PCBM solar cells. Both thin and rather thick interlayers are studied and demonstrated to work properly in organic photovoltaic. Nanocrystal V OVO layers effectively block electrons and effectively extract holes at the ITO anode. Very constant and high V (above 0.56 V) are easily achieved. Comparable J and PCE are demonstrated for nanocrystal dispersion-processed devices when compared with amorphous sol-gel processed devices. The excellent functionality of nanocrystal VO interlayers in Si-PCPDTBT:PCBM devices further demonstrates the broad application potential of this material class for photovoltaic applications. © 2012 Elsevier B.V. All rights reserved.
Keywords: Electrode buffer layer; Nanocrystals; Organic solar cell; Vanadium oxide

Nanomorphology and charge generation in bulk heterojunctions based on low-bandgap dithiophene polymers with different bridging atoms - Morana, Mauro; Azimi, Hamed; Dennler, Gilles; Egelhaaf, Hans-Joachim; Scharber, Markus; Forberich, Karen; Hauch, Jens; Gaudiana, Russell; Waller, David; Zhu, Zenghuo; Hingerl, Kurt; Van Bavel, Svetlana S.; et al. (Advanced Functional Materials, 2010)
Carbon bridged (C-PCPDTBT) and silicon-bridged (Si-PCPDTBT) dithiophene donor-acceptor copolymers belong to a promising class of low bandgap materials. Their higher field-effect mobility, as high as 10cm V s in pristine films, and their more balanced charge transport in blends with fullerenes make silicon-bridged materials better candidates for use in photovoltaic devices. Striking morphological changes are observed in polymer:fullerene bulk heterojunctions upon the substitution of the bridging atom. XRD investigation indicates increased π-π stacking in Si-PCPDTBT compared to the carbon-bridged analogue. The fluorescence of this polymer and that of its counterpart C-PCPDTBT indicates that the higher photogeneration achieved in Si-PCPDTBT:fullerene films (with either [C60]PCBM or [C70]PCBM) can be correlated to the inactivation of a charge-transfer complex and to a favorable length of the donor-acceptor phase separation. TEM studies of Si-PCPDTBT:fullerene blended films suggest the formation of an interpenetrating network whose phase distribution is comparable to the one achieved in C-PCPDTBT:fullerene using 1,8-octanedithiol as an additive. In order to achieve a balanced hole and electron transport, Si-PCPDTBT requires a lower fullerene content (between 50 to 60 wt%) than C-PCPDTBT (more than 70 wt%). The Si-PCPDTBT:[C70]PCBM OBH) solar cells deliver power conversion efficiencies of over 5%. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA.

Nano-morphology characterization of organic bulk heterojunctions based on mono and bis-adduct fullerenes - Azimi, Hamed; Fournier, Darcy; Wirix, Maarten; Dobrocka, Edmund; Ameri, Tayebeh; Machui, Florian; Rodman, Sheila; Dennler, Gilles; Scharber, Markus C.; Hingerl, Kurt; Loos, Joachim; Brabec, Christoph; et al. (Organic Electronics, 2012)
We have studied organic bulk heterojunction photovoltaic devices based on a bridged-bithiophene donor-acceptor type low-band gap polymer blended with PCBM and bis-PCBM. The impact of the molecular arrangement is discussed in terms of the correlation between the solar-cell performance and the degree of crystallization. Differential scanning calorimetry (DSC) and grazing-incidence X-ray diffraction (GIXRD) prove that films with bis-PCBM typically result in more amorphous blends than comparable films with PCBM. Electron tomography (ET) is used to visualize the three dimensional morphology of photoactive layers, confirming the presence of nanofibers, formed in different scales through the thickness in the blended films with mono and bis-fullerenes. © 2012 Elsevier B.V. All rights reserved.
Keywords: Bis-PCBM; Crystallinity; Morphology; Organic photovoltaic; PCBM

Nanoscale Morphology of Doctor Bladed versus Spin-Coated Organic Photovoltaic Films - Pokuri, Balaji Sesha Sarath; Sit, Joseph; Wodo, Olga; Baran, Derya; Ameri, Tayebeh; Brabec, Christoph; Moule, Adam J.; Ganapathysubramanian, Baskar (Advanced Energy Materials, 2017)
Recent advances in efficiency of organic photovoltaics are driven by judicious selection of processing conditions that result in a “desired” morphology. An important theme of morphology research is quantifying the effect of processing conditions on morphology and relating it to device efficiency. State-of-the-art morphology quantification methods provide film-averaged or 2D-projected features that only indirectly correlate with performance, making causal reasoning nontrivial. Accessing the 3D distribution of material, however, provides a means of directly mapping processing to performance. In this paper, two recently developed techniques are integrated—reconstruction of 3D morphology and subsequent conversion into intuitive morphology descriptors —to comprehensively image and quantify morphology. These techniques are applied on films generated by doctor blading and spin coating, additionally investigating the effect of thermal annealing. It is found that morphology of all samples exhibits very high connectivity to electrodes. Not surprisingly, thermal annealing consistently increases the average domain size in the samples, aiding exciton generation. Furthermore, annealing also improves the balance of interfaces, enhancing exciton dissociation. A comparison of morphology descriptors impacting each stage of photophysics (exciton generation, dissociation, and charge transport) reveals that spin-annealed sample exhibits superior morphology-based performance indicators. This suggests substantial room for improvement of blade-based methods (process optimization) for morphology tuning to enhance performance of large area devices.
Keywords: blade spin as-cast anneal; internal morphology analysis; organic photovoltaic cells; reconstruction; tortuosity connectivity fraction

Nanoscale Morphology of PTB7 Based Organic Photovoltaics as a Function of Fullerene Size - Roehling, John D.; Baran, Derya; Sit, Joseph; Kassar, Thaer; Ameri, Tayebeh; Unruh, Tobias; Brabec, Christoph; Moule, Adam J. (Scientific Reports, 2016)
High efficiency polymer:fullerene photovoltaic device layers self-assemble with hierarchical features from ångströms to 100's of nanometers. The feature size, shape, composition, orientation, and order all contribute to device efficiency and are simultaneously difficult to study due to poor contrast between carbon based materials. This study seeks to increase device efficiency and simplify morphology measurements by replacing the typical fullerene acceptor with endohedral fullerene LuN@PC BEH. The metal atoms give excellent scattering contrast for electron beam and X-ray experiments. Additionally, LuN@PC BEH has a lower electron affinity than standard fullerenes, which can raise the open circuit voltage of photovoltaic devices. Electron microscopy techniques are used to produce a detailed account of morphology evolution in mixtures of Lu 3 N@PC 80 BEH with the record breaking donor polymer, PTB7 and coated using solvent mixtures. We demonstrate that common solvent additives like 1,8-diiodooctane or chloronapthalene do not improve the morphology of endohedral fullerene devices as expected. The poor device performance is attributed to the lack of mutual miscibility between this particular polymer:fullerene combination and to co-crystallization of Lu 3 N@PC 80 BEH with 1,8-diiodooctane. This negative result explains why solvent additives mixtures are not necessarily a morphology cure-all.

Nanostructured organosilicon luminophores in highly efficient luminescent down-shifting layers for thin film photovoltaics - Uekert, Taylor; Solodovnyk, Anastasiia; Ponomarenko, Sergei; Osvet, Andres; Levchuk, Ievgen; Gast, Jessica; Batentschuk, Miroslaw; Forberich, Karen; Stern, Edda; Egelhaaf, Hans-Joachim; Brabec, Christoph (Solar Energy Materials and Solar Cells, 2016)
We use a new type of solution processed luminescent molecules - nanostructured organosilicon luminophores (NOLs) - in printed luminescent down-shifting layers for photovoltaic light harvesting. We show that NOLs exhibit a high luminescent efficiency of 82-90% when added into two chemically different polymer matrices that are commonly used for photovoltaic encapsulation: polyvinyl butyral and ethylene-vinyl acetate. The coated layers are optimized to maximize both UV absorbance and visible light emission and transmittance. Attaching the luminescent layers onto a CIGS solar cell significantly improves the external quantum efficiency in the UV region: from 1% to 55% at 360 nm. As a result, the short circuit current density and power conversion efficiency increase by up to 3.2-4.3%. After experimental verification of our optical simulation model, we employ it to determine the ideal molecular structure of NOLs for luminescent down-shifting applied to CIGS.
Keywords: Absorbance; CIGS; Luminescence quantum yield; Luminescent down-shifting; Organic emitter; Organosilicon nanostructure; Photovoltaics

Nanowire Interconnects for Printed Large-Area Semitransparent Organic Photovoltaic Modules - Guo, Fei; Kubis, Peter; Przybilla, Thomas; Spiecker, Erdmann; Hollmann, Andre; Langner, Stefan; Forberich, Karen; Brabec, Christoph (Advanced Energy Materials, 2015)
Semitransparent organic photovoltaic (OPV) cells promise applications in various transparent architectures where their opaque counterparts cannot contribute. Realizing practical applications of this technology requires the manufacturing of large-area modules without significant performance loss compared to the lab-scale devices. In this work, efficient semitransparent OPV modules based on ultrafast laser patterning on both glass and flexible substrates are reported. Solution-processed metallic silver nanowires (AgNWs) are used as transparent top electrodes. The efficient low-ohmic contact of the interconnects between the top AgNWs and the bottom electrode in combination with high-precision laser beam positioning system allow to fabricate semitransparent modules with high electrical fill factor of approximate to 63% and a remarkable geometric fill factor exceeding 95%, respectively. These results represent an important progress toward upscaling of high-performance OPV modules with reduced production costs.

Nb doping of TiO2 nanotubes for an enhanced efficiency of dye-sensitized solar cells - Yang, Mingjun; Kim, Dam-Hee; Jha, Himendra; Lee, Kiyoung; Paul, Jonathan; Schmuki, Patrik (Chemical Communications, 2011)
Nb-doped TiO2 nanotube (with CNb < 1 wt%) layers were successfully fabricated by self-ordered electrochemical anodization of Ti–Nb alloys. When used in dye-sensitized solar cells the efficiency enhanced by up to 30% compared to non-doped TiO2 nanotubes. IMVS measurements indicate the beneficial effect to be due to lower recombination losses.
EAM Import::2019-03-12

Near-infrared sensitization of polymer/fullerene solar cells: Controlling the morphology and transport in ternary blends - Ameri, Tayebeh; Foerster, Michael D.; Scherf, Ullrich; Brabec, Christoph (Springer New York LLC, 2017)
The concept of near-infrared (NIR) sensitization can be used as an alternative strategy to extend the spectral sensitivity of wide-bandgap polymers in polymer/fullerene solar cells. In ternary systems consisting of a conjugated polymer donor, a fullerene acceptor, and a sensitizer, the fullerene needs to act as an electron acceptor as well as an electron-transport matrix, the polymeric donor should provide a sufficiently high hole mobility, and the sensitizers should sensitize the bulk heterojunction solar cell in the red/NIR region. So far we have used various optoelectrical and structural techniques to investigate the possible mechanisms of the charge transfer and charge transport among the three components and microstructure of the ternary blends. In this review-like chapter, we present our recent achievements on developing the concept of NIR sensitization for polymer/fullerene solar cells by mainly addressing the important aspect of the relationship between morphology and transport.
Keywords: Cascade alignment; Differential scanning calorimetry; Fullerene multiadducts; GIWAXS; Hansen solubility parameters; Morphology agent; Near-IR sensitization; OPV; Phase diagram; SCLC; Surface energy; Ternary solar cell; Time-resolved pump-probe spectroscopy; Transport

Near IR sensitization of organic bulk heterojunction solar cells: Towards optimization of the spectral response of organic solar cells - Koppe, Markus; Egelhaaf, Hans-Joachim; Dennler, Gilles; Scharber, Markus C.; Brabec, Christoph; Schilinsky, Pavel; Hoth, Claudia N. (Advanced Functional Materials, 2010)
The spectroscopic response of a poly(3-hexylthiophene)/[6,6]-phenyl-C -butyric acid methyl ester (P3HT/PCBM)-based bulk heterojunction solar cell is extended into the near infrared region (NIR) of the spectrum by adding the low bandgap polymer polyp,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1 -b, 3, 4-b]-dithiophene)-alt-4, 7-(2, l, 3-benzothiadiazole)] [PCPDTBTJ to the blend. The dominant mechanism behind the enhanced photosensitivity of the ternary blend is found to be a two-step process: first, an ultrafast and efficient photoinduced charge transfer generates positive charges on P3HT and PCPDTBT and a negative charge on PCBM. In a second step, the positive charge on PCPDTBT is transferred to P3HT. Thus, P3HT serves two purposes. On the one hand it is involved in the generation of charge carriers by the photoinduced electron transfer to PCBM, and, on the other hand, it forms the charge transport matrix for the positive carriers transferred from PCPDTBT. Other mechanisms, such as energy transfer or photoinduced charge transfer directly between the two polymers, are found to be absent or negligible. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA.

Near IR sensitization of polymer/fullerene solar cells - Ameri, Tayebeh; Min, Jie; Li, Ning; Machui, Florian; Brabec, Christoph; Forster, Michael; Schottler, Kristina; Dolfen, Daniel; Allard, Sybille; Scherf, Ullrich (Organic Photovoltaics XIII, 2012)
In this work we discuss an elegant, alternative strategy to extend the spectral sensitivity of wide bandgap polymers in the near IR region. We discuss the microstructure of different functional ternary systems and compare them from different perspectives. © 2012 SPIE.
Keywords: IR sensitization; Organic solar cells; Small bandgap polymers; Ternary blends

New approaches and understandings in the growth of cubic silicon carbide - Via, Francesco La; Zimbone, Massimo; Bongiorno, Corrado; La Magna, Antonino; Fisicaro, Giuseppe; Deretzis, Ioannis; Scuderi, Viviana; Calabretta, Cristiano; Giannazzo, Filippo; Zielinski, Marcin; Anzalone, Ruggero; Mauceri, Marco; et al. (Materials, 2021)
In this review paper, several new approaches about the 3C‐SiC growth are been presented. In fact, despite the long research activity on 3C‐SiC, no devices with good electrical characteristics have been obtained due to the high defect density and high level of stress. To overcome these problems, two different approaches have been used in the last years. From one side, several compliance substrates have been used to try to reduce both the defects and stress, while from another side, the first bulk growth has been performed to try to improve the quality of this material with respect to the heteroepitaxial one. From all these studies, a new understanding of the material defects has been obtained, as well as regarding all the interactions between defects and several growth parameters. This new knowledge will be the basis to solve the main issue of the 3C‐SiC growth and reach the goal to obtain a material with low defects and low stress that would allow for realizing devices with extremely interesting characteristics.
CRIS-Team Scopus Importer:2021-10-01
Keywords: 3C‐SiC; Bulk growth; Compliant substrates; Defects; Heteroepitaxy; Stress